msleep() in interrupt handler?
Hi List, What will happen if call msleep() in an interrupt handler? I knew the msleep() will cause the calling process to sleep, but in the context of interruption, there is no process, so I am wondering what is getting 'sleep' in this situation. -woody -- Sent from Gmail Mobile
From: kernelnewbies-bounces@kernelnewbies.org [mailto:kernelnewbies-bounces@kernelnewbies.org] On Behalf Of Woody Wu Sent: Wednesday, August 19, 2015 4:47 PM To: kernelnewbies Subject: msleep() in interrupt handler? Hi List, What will happen if call msleep() in an interrupt handler? I knew the msleep() will cause the calling process to sleep, but in the context of interruption, there is no process, so I am wondering what is getting 'sleep' in this situation. -woody -- Sent from Gmail Mobile If you are lucky you’ll get a message along the lines of “scheduling while atomic” on your console to let you know you’ve blown it. At least that’s what I’ve seen when I’ve blown it like that. 8^) Jeff Haran
On Thursday, August 20, 2015, Jeff Haran <Jeff.Haran@citrix.com> wrote:
*From:* kernelnewbies-bounces@kernelnewbies.org <javascript:_e(%7B%7D,'cvml','kernelnewbies-bounces@kernelnewbies.org');> [mailto:kernelnewbies-bounces@kernelnewbies.org <javascript:_e(%7B%7D,'cvml','kernelnewbies-bounces@kernelnewbies.org');>] *On Behalf Of *Woody Wu *Sent:* Wednesday, August 19, 2015 4:47 PM *To:* kernelnewbies *Subject:* msleep() in interrupt handler?
Hi List,
What will happen if call msleep() in an interrupt handler? I knew the msleep() will cause the calling process to sleep, but in the context of interruption, there is no process, so I am wondering what is getting 'sleep' in this situation.
-woody
-- Sent from Gmail Mobile
If you are lucky you’ll get a message along the lines of “scheduling while atomic” on your console to let you know you’ve blown it. At least that’s what I’ve seen when I’ve blown it like that. 8^)
Jeff Haran
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous? -- Sent from Gmail Mobile
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c Thanks in advance. -woody -- Sent from Gmail Mobile
On 15-08-20 19:02:50, Woody Wu wrote:
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c
I checked the code. The kernel release I am checking in is 4.1.5. From what I can see there is only atmel_mxt_ts.c and not atmel_mXT224_ts.c in drivers/ input/touchscreen. In this code, it is requesting a threaded irq with the top handler being specified as null and the bottom handler specified. Since the bottom handler is being used where i2c_transfer is called and as such though on a quick check I do not see the msleep() call, even if the msleep were called while in the bottom handler context it would be fine. I do not know which code you are referring to but in hard interrupt context atleast you can never ever call any function which can sleep. It is just gonna blow in some way. - Sanchayan.
On Thursday, August 20, 2015, <victorascroft@gmail.com> wrote:
On 15-08-20 19:02:50, Woody Wu wrote:
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com <javascript:;>> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c
I checked the code. The kernel release I am checking in is 4.1.5. From what I can see there is only atmel_mxt_ts.c and not atmel_mXT224_ts.c in drivers/ input/touchscreen. In this code, it is requesting a threaded irq with the top handler being specified as null and the bottom handler specified.
Since the bottom handler is being used where i2c_transfer is called and as such though on a quick check I do not see the msleep() call, even if the msleep were called while in the bottom handler context it would be fine.
I do not know which code you are referring to but in hard interrupt context atleast you can never ever call any function which can sleep. It is just gonna blow in some way.
- Sanchayan.
The file name you said is right. The kernel version I am using is 3.1.x, but I guess it does no much matter to the question. The interrupt handler of the atmel_mxt_ts called i2c_transfer() which indeed called the actual i2c adapter's transfer method. In my platform, the i2c adapter is a s3c i2c controller, so I was checking the code in i2c/busses/i2c_s3c.c, from this file I saw the msleep() was called in i2c_doxfer()->i2c_set_master() call sequence. I think you can find he similar things in 4.1.5. Thanks. -woody -- Sent from Gmail Mobile
On 15-08-20 21:44:14, Woody Wu wrote:
On Thursday, August 20, 2015, <victorascroft@gmail.com> wrote:
On 15-08-20 19:02:50, Woody Wu wrote:
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com <javascript:;>> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c
I checked the code. The kernel release I am checking in is 4.1.5. From what I can see there is only atmel_mxt_ts.c and not atmel_mXT224_ts.c in drivers/ input/touchscreen. In this code, it is requesting a threaded irq with the top handler being specified as null and the bottom handler specified.
Since the bottom handler is being used where i2c_transfer is called and as such though on a quick check I do not see the msleep() call, even if the msleep were called while in the bottom handler context it would be fine.
I do not know which code you are referring to but in hard interrupt context atleast you can never ever call any function which can sleep. It is just gonna blow in some way.
- Sanchayan.
The file name you said is right. The kernel version I am using is 3.1.x, but I guess it does no much matter to the question. The interrupt handler of the atmel_mxt_ts called i2c_transfer() which indeed called the actual i2c adapter's transfer method. In my platform, the i2c adapter is a s3c i2c controller, so I was checking the code in i2c/busses/i2c_s3c.c, from this file I saw the msleep() was called in i2c_doxfer()->i2c_set_master() call sequence. I think you can find he similar things in 4.1.5.
Yes right atmel_mxt_ts does call i2c_transfer. I did not check myself but even if the call chain results in msleep() getting called somewhere this would not be in the top irq handler. So mlseep() is ok. Had this been in top irq handler (which it will never be in the kernel) then it will just not work at all as the kernel will crash. Check all drivers in touchscreen. All of them do not use the top irq handler and use a bottom handler specified with threaded irq request. So it is fine if msleep() is getting called somewhere down that line. Also as far as I know none of the touchscreen drivers in drivers/input/touchscreen use the irq handler plus workqueue approach anymore. Also if one were to try and submit such a one to the mainline you will be just asked to convert to a threaded irq approach. Just some info since I saw a recommendation on going with irq + workqueue approach. However I dont know if threaded irqs existed in 3.1.x. - Sanchayan.
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 9:42 AM To: Woody Wu Cc: John de la Garza; Jeff Haran; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 21:44:14, Woody Wu wrote:
On Thursday, August 20, 2015, <victorascroft@gmail.com> wrote:
On 15-08-20 19:02:50, Woody Wu wrote:
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com <javascript:;>> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c
I checked the code. The kernel release I am checking in is 4.1.5. From what I can see there is only atmel_mxt_ts.c and not atmel_mXT224_ts.c in drivers/ input/touchscreen. In this code, it is requesting a threaded irq with the top handler being specified as null and the bottom handler specified.
Since the bottom handler is being used where i2c_transfer is called and as such though on a quick check I do not see the msleep() call, even if the msleep were called while in the bottom handler context it would be fine.
I do not know which code you are referring to but in hard interrupt context atleast you can never ever call any function which can sleep. It is just gonna blow in some way.
- Sanchayan.
The file name you said is right. The kernel version I am using is 3.1.x, but I guess it does no much matter to the question. The interrupt handler of the atmel_mxt_ts called i2c_transfer() which indeed called the actual i2c adapter's transfer method. In my platform, the i2c adapter is a s3c i2c controller, so I was checking the code in i2c/busses/i2c_s3c.c, from this file I saw the msleep() was called in i2c_doxfer()->i2c_set_master() call sequence. I think you can find he similar things in 4.1.5.
Yes right atmel_mxt_ts does call i2c_transfer. I did not check myself but even if the call chain results in msleep() getting called somewhere this would not be in the top irq handler. So mlseep() is ok. Had this been in top irq handler (which it will never be in the kernel) then it will just not work at all as the kernel will crash.
Check all drivers in touchscreen. All of them do not use the top irq handler and use a bottom handler specified with threaded irq request. So it is fine if msleep() is getting called somewhere down that line.
Perhaps I misread the msleep() code, but it appeared to me that it resulted in a call to schedule(). If you are executing in bottom half context and call a kernel function that results in a scheduling, what returns execution to the bottom half after schedule()? There's no task control block behind a bottom half to return control to, is there?
Also as far as I know none of the touchscreen drivers in drivers/input/touchscreen use the irq handler plus workqueue approach anymore. Also if one were to try and submit such a one to the mainline you will be just asked to convert to a threaded irq approach. Just some info since I saw a recommendation on going with irq + workqueue approach. However I dont know if threaded irqs existed in 3.1.x.
- Sanchayan.
On 15-08-20 16:54:26, Jeff Haran wrote:
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 9:42 AM To: Woody Wu Cc: John de la Garza; Jeff Haran; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 21:44:14, Woody Wu wrote:
On Thursday, August 20, 2015, <victorascroft@gmail.com> wrote:
On 15-08-20 19:02:50, Woody Wu wrote:
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com <javascript:;>> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c
I checked the code. The kernel release I am checking in is 4.1.5. From what I can see there is only atmel_mxt_ts.c and not atmel_mXT224_ts.c in drivers/ input/touchscreen. In this code, it is requesting a threaded irq with the top handler being specified as null and the bottom handler specified.
Since the bottom handler is being used where i2c_transfer is called and as such though on a quick check I do not see the msleep() call, even if the msleep were called while in the bottom handler context it would be fine.
I do not know which code you are referring to but in hard interrupt context atleast you can never ever call any function which can sleep. It is just gonna blow in some way.
- Sanchayan.
The file name you said is right. The kernel version I am using is 3.1.x, but I guess it does no much matter to the question. The interrupt handler of the atmel_mxt_ts called i2c_transfer() which indeed called the actual i2c adapter's transfer method. In my platform, the i2c adapter is a s3c i2c controller, so I was checking the code in i2c/busses/i2c_s3c.c, from this file I saw the msleep() was called in i2c_doxfer()->i2c_set_master() call sequence. I think you can find he similar things in 4.1.5.
Yes right atmel_mxt_ts does call i2c_transfer. I did not check myself but even if the call chain results in msleep() getting called somewhere this would not be in the top irq handler. So mlseep() is ok. Had this been in top irq handler (which it will never be in the kernel) then it will just not work at all as the kernel will crash.
Check all drivers in touchscreen. All of them do not use the top irq handler and use a bottom handler specified with threaded irq request. So it is fine if msleep() is getting called somewhere down that line.
Perhaps I misread the msleep() code, but it appeared to me that it resulted in a call to schedule(). If you are executing in bottom half context and call a kernel function that results in a scheduling, what returns execution to the bottom half after schedule()? There's no task control block behind a bottom half to return control to, is there?
Nice question. Thanks for asking. It made me look at that code for the first time. Frankly I accept I do not know. But here goes. The call chain is as follows: msleep() schedule_timeout_uninterruptible() schedule_timeout()
From here it sets up a timer and calls schedule() In schedule(), we take task_struct as the current one submit this task and then call __schedule() (The comments above this one are worth reading)
I believe this will definitely return control back from what I understand once this task is scheduled back. -- Sanchayan.
Also as far as I know none of the touchscreen drivers in drivers/input/touchscreen use the irq handler plus workqueue approach anymore. Also if one were to try and submit such a one to the mainline you will be just asked to convert to a threaded irq approach. Just some info since I saw a recommendation on going with irq + workqueue approach. However I dont know if threaded irqs existed in 3.1.x.
- Sanchayan.
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 10:50 AM To: Jeff Haran Cc: Woody Wu; John de la Garza; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 16:54:26, Jeff Haran wrote:
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 9:42 AM To: Woody Wu Cc: John de la Garza; Jeff Haran; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 21:44:14, Woody Wu wrote:
On Thursday, August 20, 2015, <victorascroft@gmail.com> wrote:
On 15-08-20 19:02:50, Woody Wu wrote:
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com <javascript:;>> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c
I checked the code. The kernel release I am checking in is 4.1.5. From what I can see there is only atmel_mxt_ts.c and not atmel_mXT224_ts.c in drivers/ input/touchscreen. In this code, it is requesting a threaded irq with the top handler being specified as null and the bottom handler specified.
Since the bottom handler is being used where i2c_transfer is called and as such though on a quick check I do not see the msleep() call, even if the msleep were called while in the bottom handler context it would be fine.
I do not know which code you are referring to but in hard interrupt context atleast you can never ever call any function which can sleep. It is just gonna blow in some way.
- Sanchayan.
The file name you said is right. The kernel version I am using is 3.1.x, but I guess it does no much matter to the question. The interrupt handler of the atmel_mxt_ts called i2c_transfer() which indeed called the actual i2c adapter's transfer method. In my platform, the i2c adapter is a s3c i2c controller, so I was checking the code in i2c/busses/i2c_s3c.c, from this file I saw the msleep() was called in i2c_doxfer()->i2c_set_master() call sequence. I think you can find he similar things in 4.1.5.
Yes right atmel_mxt_ts does call i2c_transfer. I did not check myself but even if the call chain results in msleep() getting called somewhere this would not be in the top irq handler. So mlseep() is ok. Had this been in top irq handler (which it will never be in the kernel) then it will just not work at all as the kernel will crash.
Check all drivers in touchscreen. All of them do not use the top irq handler and use a bottom handler specified with threaded irq request. So it is fine if msleep() is getting called somewhere down that line.
Perhaps I misread the msleep() code, but it appeared to me that it resulted in a call to schedule(). If you are executing in bottom half context and call a kernel function that results in a scheduling, what returns execution to the bottom half after schedule()? There's no task control block behind a bottom half to return control to, is there?
Nice question. Thanks for asking. It made me look at that code for the first time. Frankly I accept I do not know. But here goes.
The call chain is as follows: msleep() schedule_timeout_uninterruptible() schedule_timeout() From here it sets up a timer and calls schedule() In schedule(), we take task_struct as the current one submit this task and then call __schedule() (The comments above this one are worth reading)
I believe this will definitely return control back from what I understand once this task is scheduled back.
-- Sanchayan.
But the current task_struct will be whatever task happened to be running when the soft IRQ went off. Execution won't return to the soft IRQ code that called msleep() because soft IRQs aren't tasks. When soft IRQs are running under ksoftirqd it might work, but that's the exception. Take a look at this call tree: schedule() -> __schedule() -> schedule_debug() 2631 /* 2632 * Various schedule()-time debugging checks and statistics: 2633 */ 2634 static inline void schedule_debug(struct task_struct *prev) 2635 { 2636 #ifdef CONFIG_SCHED_STACK_END_CHECK 2637 BUG_ON(unlikely(task_stack_end_corrupted(prev))); 2638 #endif 2639 /* 2640 * Test if we are atomic. Since do_exit() needs to call into 2641 * schedule() atomically, we ignore that path. Otherwise whine 2642 * if we are scheduling when we should not. 2643 */ 2644 if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD)) 2645 __schedule_bug(prev); 2646 rcu_sleep_check(); 2647 2648 profile_hit(SCHED_PROFILING, __builtin_return_address(0)); 2649 2650 schedstat_inc(this_rq(), sched_count); 2651 } The last time I looked at this in any detail (which was admittedly quite a while ago), in_atomic_preempt_off() would return true when called by a soft IRQ, but it could have changed since then. Jeff Haran
Also as far as I know none of the touchscreen drivers in drivers/input/touchscreen use the irq handler plus workqueue approach anymore. Also if one were to try and submit such a one to the mainline you will be just asked to convert to a threaded irq approach. Just some info since I saw a recommendation on going with irq + workqueue approach. However I dont know if threaded irqs existed
in 3.1.x.
- Sanchayan.
On 15-08-20 18:16:02, Jeff Haran wrote:
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 10:50 AM To: Jeff Haran Cc: Woody Wu; John de la Garza; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 16:54:26, Jeff Haran wrote:
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 9:42 AM To: Woody Wu Cc: John de la Garza; Jeff Haran; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 21:44:14, Woody Wu wrote:
On Thursday, August 20, 2015, <victorascroft@gmail.com> wrote:
On 15-08-20 19:02:50, Woody Wu wrote:
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com <javascript:;>> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c
I checked the code. The kernel release I am checking in is 4.1.5. From what I can see there is only atmel_mxt_ts.c and not atmel_mXT224_ts.c in drivers/ input/touchscreen. In this code, it is requesting a threaded irq with the top handler being specified as null and the bottom handler specified.
Since the bottom handler is being used where i2c_transfer is called and as such though on a quick check I do not see the msleep() call, even if the msleep were called while in the bottom handler context it would be fine.
I do not know which code you are referring to but in hard interrupt context atleast you can never ever call any function which can sleep. It is just gonna blow in some way.
- Sanchayan.
The file name you said is right. The kernel version I am using is 3.1.x, but I guess it does no much matter to the question. The interrupt handler of the atmel_mxt_ts called i2c_transfer() which indeed called the actual i2c adapter's transfer method. In my platform, the i2c adapter is a s3c i2c controller, so I was checking the code in i2c/busses/i2c_s3c.c, from this file I saw the msleep() was called in i2c_doxfer()->i2c_set_master() call sequence. I think you can find he similar things in 4.1.5.
Yes right atmel_mxt_ts does call i2c_transfer. I did not check myself but even if the call chain results in msleep() getting called somewhere this would not be in the top irq handler. So mlseep() is ok. Had this been in top irq handler (which it will never be in the kernel) then it will just not work at all as the kernel will crash.
Check all drivers in touchscreen. All of them do not use the top irq handler and use a bottom handler specified with threaded irq request. So it is fine if msleep() is getting called somewhere down that line.
Perhaps I misread the msleep() code, but it appeared to me that it resulted in a call to schedule(). If you are executing in bottom half context and call a kernel function that results in a scheduling, what returns execution to the bottom half after schedule()? There's no task control block behind a bottom half to return control to, is there?
Nice question. Thanks for asking. It made me look at that code for the first time. Frankly I accept I do not know. But here goes.
The call chain is as follows: msleep() schedule_timeout_uninterruptible() schedule_timeout() From here it sets up a timer and calls schedule() In schedule(), we take task_struct as the current one submit this task and then call __schedule() (The comments above this one are worth reading)
I believe this will definitely return control back from what I understand once this task is scheduled back.
-- Sanchayan.
But the current task_struct will be whatever task happened to be running when the soft IRQ went off. Execution won't return to the soft IRQ code that called msleep() because soft IRQs aren't tasks. When soft IRQs are running under ksoftirqd it might work, but that's the exception. Take a look at this call tree:
The thread handler function which is setup by the request threaded irq is a kernel thread. The kernel thread I talk of here isn't the soft irq you are speaking of. Kernel thread can run in process context as far as I know the last time I looked up. So on sleeping and getting scheduled, it definitiely has a context it can return back to. Now this place I do not have the code to trace and only know in theory or atleast I am not sure if I am looking at the correct place. request_threaded_irq __setup_irq This shows a task struct being associated with the irqaction. So the kernel thread definitely has a process context. As long as there is a process context we can definitely return from a msleep()->schedule()->__schedule. -- Sanchayan.
schedule() -> __schedule() -> schedule_debug()
2631 /* 2632 * Various schedule()-time debugging checks and statistics: 2633 */ 2634 static inline void schedule_debug(struct task_struct *prev) 2635 { 2636 #ifdef CONFIG_SCHED_STACK_END_CHECK 2637 BUG_ON(unlikely(task_stack_end_corrupted(prev))); 2638 #endif 2639 /* 2640 * Test if we are atomic. Since do_exit() needs to call into 2641 * schedule() atomically, we ignore that path. Otherwise whine 2642 * if we are scheduling when we should not. 2643 */ 2644 if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD)) 2645 __schedule_bug(prev); 2646 rcu_sleep_check(); 2647 2648 profile_hit(SCHED_PROFILING, __builtin_return_address(0)); 2649 2650 schedstat_inc(this_rq(), sched_count); 2651 }
The last time I looked at this in any detail (which was admittedly quite a while ago), in_atomic_preempt_off() would return true when called by a soft IRQ, but it could have changed since then.
Jeff Haran
Also as far as I know none of the touchscreen drivers in drivers/input/touchscreen use the irq handler plus workqueue approach anymore. Also if one were to try and submit such a one to the mainline you will be just asked to convert to a threaded irq approach. Just some info since I saw a recommendation on going with irq + workqueue approach. However I dont know if threaded irqs existed
in 3.1.x.
- Sanchayan.
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 12:16 PM To: Jeff Haran Cc: Woody Wu; John de la Garza; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 18:16:02, Jeff Haran wrote:
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 10:50 AM To: Jeff Haran Cc: Woody Wu; John de la Garza; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 16:54:26, Jeff Haran wrote:
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 9:42 AM To: Woody Wu Cc: John de la Garza; Jeff Haran; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 21:44:14, Woody Wu wrote:
On Thursday, August 20, 2015, <victorascroft@gmail.com> wrote:
On 15-08-20 19:02:50, Woody Wu wrote:
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com <javascript:;>> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c
I checked the code. The kernel release I am checking in is 4.1.5. From what I can see there is only atmel_mxt_ts.c and not atmel_mXT224_ts.c in drivers/ input/touchscreen. In this code, it is requesting a threaded irq with the top handler being specified as null and the bottom handler specified.
Since the bottom handler is being used where i2c_transfer is called and as such though on a quick check I do not see the msleep() call, even if the msleep were called while in the bottom handler context it would be fine.
I do not know which code you are referring to but in hard interrupt context atleast you can never ever call any function which can sleep. It is just gonna blow in some way.
- Sanchayan.
The file name you said is right. The kernel version I am using is 3.1.x, but I guess it does no much matter to the question. The interrupt handler of the atmel_mxt_ts called i2c_transfer() which indeed called the actual i2c adapter's transfer method. In my platform, the i2c adapter is a s3c i2c controller, so I was checking the code in i2c/busses/i2c_s3c.c, from this file I saw the msleep() was called in i2c_doxfer()->i2c_set_master() call sequence. I think you can find he similar things in 4.1.5.
Yes right atmel_mxt_ts does call i2c_transfer. I did not check myself but even if the call chain results in msleep() getting called somewhere this would not be in the top irq handler. So mlseep() is ok. Had this been in top irq handler (which it will never be in the kernel) then it will just not work at all as the kernel will crash.
Check all drivers in touchscreen. All of them do not use the top irq handler and use a bottom handler specified with threaded irq request. So it is fine if msleep() is getting called somewhere down that line.
Perhaps I misread the msleep() code, but it appeared to me that it resulted in a call to schedule(). If you are executing in bottom half context and call a kernel function that results in a scheduling, what returns execution to the bottom half after schedule()? There's no task control block behind a bottom half to return control to, is there?
Nice question. Thanks for asking. It made me look at that code for the first time. Frankly I accept I do not know. But here goes.
The call chain is as follows: msleep() schedule_timeout_uninterruptible() schedule_timeout() From here it sets up a timer and calls schedule() In schedule(), we take task_struct as the current one submit this task and then call __schedule() (The comments above this one are worth reading)
I believe this will definitely return control back from what I understand once this task is scheduled back.
-- Sanchayan.
But the current task_struct will be whatever task happened to be running when the soft IRQ went off. Execution won't return to the soft IRQ code that called msleep() because soft IRQs aren't tasks. When soft IRQs are running under ksoftirqd it might work, but that's the exception. Take a look at this call tree:
The thread handler function which is setup by the request threaded irq is a kernel thread. The kernel thread I talk of here isn't the soft irq you are speaking of. Kernel thread can run in process context as far as I know the last time I looked up. So on sleeping and getting scheduled, it definitiely has a context it can return back to. Now this place I do not have the code to trace and only know in theory or atleast I am not sure if I am looking at the correct place.
request_threaded_irq __setup_irq
This shows a task struct being associated with the irqaction. So the kernel thread definitely has a process context. As long as there is a process context we can definitely return from a msleep()->schedule()->__schedule.
-- Sanchayan.
OK, I see the source of my confusion. When I read "bottom handler" in your original post I assumed you were referring to bottom halves as in soft IRQs and missed the threaded IRQ bit. My apologies for the distraction and thanks for clarifying this. Jeff Haran
schedule() -> __schedule() -> schedule_debug()
2631 /* 2632 * Various schedule()-time debugging checks and statistics: 2633 */ 2634 static inline void schedule_debug(struct task_struct *prev) 2635 { 2636 #ifdef CONFIG_SCHED_STACK_END_CHECK 2637 BUG_ON(unlikely(task_stack_end_corrupted(prev))); 2638 #endif 2639 /* 2640 * Test if we are atomic. Since do_exit() needs to call into 2641 * schedule() atomically, we ignore that path. Otherwise whine 2642 * if we are scheduling when we should not. 2643 */ 2644 if (unlikely(in_atomic_preempt_off() && prev->state !=
TASK_DEAD))
2645 __schedule_bug(prev); 2646 rcu_sleep_check(); 2647 2648 profile_hit(SCHED_PROFILING, __builtin_return_address(0)); 2649 2650 schedstat_inc(this_rq(), sched_count); 2651 }
The last time I looked at this in any detail (which was admittedly quite a while ago), in_atomic_preempt_off() would return true when called by a soft IRQ, but it could have changed since then.
Jeff Haran
Also as far as I know none of the touchscreen drivers in drivers/input/touchscreen use the irq handler plus workqueue approach anymore. Also if one were to try and submit such a one to the mainline you will be just asked to convert to a threaded irq approach. Just some info since I saw a recommendation on going with irq + workqueue approach. However I dont know if threaded irqs existed
in 3.1.x.
- Sanchayan.
On 15-08-20 19:36:23, Jeff Haran wrote:
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 12:16 PM To: Jeff Haran Cc: Woody Wu; John de la Garza; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 18:16:02, Jeff Haran wrote:
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 10:50 AM To: Jeff Haran Cc: Woody Wu; John de la Garza; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 16:54:26, Jeff Haran wrote:
-----Original Message----- From: victorascroft@gmail.com [mailto:victorascroft@gmail.com] Sent: Thursday, August 20, 2015 9:42 AM To: Woody Wu Cc: John de la Garza; Jeff Haran; kernelnewbies Subject: Re: msleep() in interrupt handler?
On 15-08-20 21:44:14, Woody Wu wrote:
On Thursday, August 20, 2015, <victorascroft@gmail.com> wrote:
On 15-08-20 19:02:50, Woody Wu wrote:
On Thursday, August 20, 2015, John de la Garza <john@jjdev.com <javascript:;>> wrote:
On Thu, Aug 20, 2015 at 01:45:34PM +0800, Woody Wu wrote:
I did not see the message. Actually my interrupt handler is calling i2c_transfer which in turn used msleep() somewhere in its code. Is this normal or dangerous?
Can you have the interrupt handler put the work on a workqueue and quickly return?
Yes, that is an option. But I firstly need to know the old code is really bad. The interrupt is triggered by an i2c touchscreen, and the interrupt handler use the i2c core code to start the i2c transferring. I see in the i2c adapter code a msleep() was invoked at beginning of transfer. I doubt that this is a potential problem. But you know the i2c touchscreen driver code is also part of the mainline, so I am not sure my option. You guys can check the code of atmel_mXT224_ts.c, the i2c adapter code is i2c_s3c.c
I checked the code. The kernel release I am checking in is 4.1.5. From what I can see there is only atmel_mxt_ts.c and not atmel_mXT224_ts.c in drivers/ input/touchscreen. In this code, it is requesting a threaded irq with the top handler being specified as null and the bottom handler specified.
Since the bottom handler is being used where i2c_transfer is called and as such though on a quick check I do not see the msleep() call, even if the msleep were called while in the bottom handler context it would be fine.
I do not know which code you are referring to but in hard interrupt context atleast you can never ever call any function which can sleep. It is just gonna blow in some way.
- Sanchayan.
The file name you said is right. The kernel version I am using is 3.1.x, but I guess it does no much matter to the question. The interrupt handler of the atmel_mxt_ts called i2c_transfer() which indeed called the actual i2c adapter's transfer method. In my platform, the i2c adapter is a s3c i2c controller, so I was checking the code in i2c/busses/i2c_s3c.c, from this file I saw the msleep() was called in i2c_doxfer()->i2c_set_master() call sequence. I think you can find he similar things in 4.1.5.
Yes right atmel_mxt_ts does call i2c_transfer. I did not check myself but even if the call chain results in msleep() getting called somewhere this would not be in the top irq handler. So mlseep() is ok. Had this been in top irq handler (which it will never be in the kernel) then it will just not work at all as the kernel will crash.
Check all drivers in touchscreen. All of them do not use the top irq handler and use a bottom handler specified with threaded irq request. So it is fine if msleep() is getting called somewhere down that line.
Perhaps I misread the msleep() code, but it appeared to me that it resulted in a call to schedule(). If you are executing in bottom half context and call a kernel function that results in a scheduling, what returns execution to the bottom half after schedule()? There's no task control block behind a bottom half to return control to, is there?
Nice question. Thanks for asking. It made me look at that code for the first time. Frankly I accept I do not know. But here goes.
The call chain is as follows: msleep() schedule_timeout_uninterruptible() schedule_timeout() From here it sets up a timer and calls schedule() In schedule(), we take task_struct as the current one submit this task and then call __schedule() (The comments above this one are worth reading)
I believe this will definitely return control back from what I understand once this task is scheduled back.
-- Sanchayan.
But the current task_struct will be whatever task happened to be running when the soft IRQ went off. Execution won't return to the soft IRQ code that called msleep() because soft IRQs aren't tasks. When soft IRQs are running under ksoftirqd it might work, but that's the exception. Take a look at this call tree:
The thread handler function which is setup by the request threaded irq is a kernel thread. The kernel thread I talk of here isn't the soft irq you are speaking of. Kernel thread can run in process context as far as I know the last time I looked up. So on sleeping and getting scheduled, it definitiely has a context it can return back to. Now this place I do not have the code to trace and only know in theory or atleast I am not sure if I am looking at the correct place.
request_threaded_irq __setup_irq
This shows a task struct being associated with the irqaction. So the kernel thread definitely has a process context. As long as there is a process context we can definitely return from a msleep()->schedule()->__schedule.
-- Sanchayan.
OK, I see the source of my confusion. When I read "bottom handler" in your original post I assumed you were referring to bottom halves as in soft IRQs and missed the threaded IRQ bit.
My apologies for the distraction and thanks for clarifying this.
No problem at all. It was an interesting discussion and I got to learn what I wrote. Thanks. Cheers. - Sanchayan.
Jeff Haran
schedule() -> __schedule() -> schedule_debug()
2631 /* 2632 * Various schedule()-time debugging checks and statistics: 2633 */ 2634 static inline void schedule_debug(struct task_struct *prev) 2635 { 2636 #ifdef CONFIG_SCHED_STACK_END_CHECK 2637 BUG_ON(unlikely(task_stack_end_corrupted(prev))); 2638 #endif 2639 /* 2640 * Test if we are atomic. Since do_exit() needs to call into 2641 * schedule() atomically, we ignore that path. Otherwise whine 2642 * if we are scheduling when we should not. 2643 */ 2644 if (unlikely(in_atomic_preempt_off() && prev->state !=
TASK_DEAD))
2645 __schedule_bug(prev); 2646 rcu_sleep_check(); 2647 2648 profile_hit(SCHED_PROFILING, __builtin_return_address(0)); 2649 2650 schedstat_inc(this_rq(), sched_count); 2651 }
The last time I looked at this in any detail (which was admittedly quite a while ago), in_atomic_preempt_off() would return true when called by a soft IRQ, but it could have changed since then.
Jeff Haran
Also as far as I know none of the touchscreen drivers in drivers/input/touchscreen use the irq handler plus workqueue approach anymore. Also if one were to try and submit such a one to the mainline you will be just asked to convert to a threaded irq approach. Just some info since I saw a recommendation on going with irq + workqueue approach. However I dont know if threaded irqs existed
in 3.1.x.
- Sanchayan.
participants (4)
-
Jeff Haran -
John de la Garza -
victorascroft＠gmail.com -
Woody Wu