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RE: spinlock deadlock
by buyitian Feb. 18, 2013

Feb. 18, 2013

> Date: Mon, 18 Feb 2013 10:54:44 +0100 > From: tglx(a)linutronix.de > To: buyit(a)live.cn > CC: mulyadi.santosa(a)gmail.com; kernelnewbies(a)kernelnewbies.org; a.p.zijlstra(a)chello.nl; rabin(a)rab.in; mingo(a)kernel.org > Subject: RE: spinlock deadlock > > On Sun, 17 Feb 2013, buyitian wrote: > > Could you please use a mail client, which creates readable mail? > > > this patch is to prevent deadlock between rq->lock and > > logbuf_lock. i can understand this thanks to Rabin. 2. in patch > > 07354eb1a74d1e1ece29f8bafe0b46e8c77a95ef, Thomas did changes as > > below, which reverted the change from peter, i don't know why: in > > function console_trylock_for_printk(): > > > - spin_unlock(&logbuf_lock); > > if (wake) > > up(&console_sem); > > + raw_spin_unlock(&logbuf_lock); > > > and this change exists in the latest kernel source code. it seems > > that deadlock bewteen rq->lock and logbuf_lock comes back, who can > > explain this, thanks. BTW: if i place printk inside schedule(), i > > may get rq->lock before calling printk. > > That looks like a merge slipup. The patch which converts the lock is > not supposed to do any other changes. But the patch was based on an > older kernel version, which did not have Peters changes yet. So the > fixup of the not longer applying patch failed somehow. i will provide patch, thanks for your reply. > > Thanks, > > tglx

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sizeof(int[1]) means what ?
by sdptroy3＠gmail.com Feb. 17, 2013

Feb. 17, 2013

hi, i'm reading the file ioctl.h, there i encountered a macro _IOC_TYPECHECK(t) which looks like: #define _IOC_TYPECHECK(t) \ ((sizeof(t) == sizeof(t[1]) && \ sizeof(t) < (1 << _IOC_SIZEBITS)) ? \ sizeof(t) : __invalid_size_argument_for_IOC) in this code ,what does sizeof(t[1]) mean? i mean the argument of this macro in a type(int, float), in that case what does sizeof(int[1]) specify? I have written a small test program which prints the value of the expression 4. Thank you

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Is there someone farmiliar with bochs source code ?
by horseriver Feb. 17, 2013

Feb. 17, 2013

hi:) I am doing research on bochs , want to get some help from you. Any help will be appreciate. BX_CPU_C::fetchDecode32(const Bit8u *iptr, bxInstruction_c *i, unsigned remainingInPage) 1.what is the meaning of ths iptr parameter? Is the content pointed by it a executable text region? thanks!

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spinlock deadlock
by buyitian Feb. 17, 2013

Feb. 17, 2013

is it possible that printk cause deadlock? the path is as below: 1. taskA runs on CPU0, and run schedule to acqire the rq->lock.2. taskA calls printk while holding rq->lock.3. taskA holds console_sem.4. taskB runs on CPU1, and call console_lock(), which is blocked by console_sem and queue itslef to the wait list.5. taskB migrates from CPU1 to cpu0. will this step occur?6. taskA calls up(&console_sem)--> wake_up_process()-->try_to_wake_up()-->ttwu_queue()-->raw_spin_lock(&rq->lock). here taskA tries to acquire the rq->lock of CPU0 again.

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process 0 ("swapper")
by Kevin Wilson Feb. 17, 2013

Feb. 17, 2013

Hi, I see that the idle process (process 0) , is called "swapper". init_idle() in kernel/sched/core.c: ... #if defined(CONFIG_SMP) sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu); #endif ... #define INIT_TASK_COMM "swapper" in include/linux/init_task.h Two questions: 1) why does this #if defined(CONFIG_SMP) here ? shouldn't we name it swapper also in non SMP mode ? 2) Is there a reason that we do not see it with ps aux (and also not under proc; there is no /proc/0). - 1) no process 0; processes start from "1". - 2) following command gives nothing: ps aux | grep -i swapper rgs, Kevin

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How to solve module collision
by Jimmy Pan Feb. 16, 2013

Feb. 16, 2013

Hi, I would like to write a driver for my usb mouse. It functions normally with kernel driver, nonetheless, I want to study usb system. When the kernel executes the probe function, what would happen if there exists two suitable drivers. And how can I override the existed kernel driver? I presume that

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using prefetch
by Kevin Wilson Feb. 15, 2013

Feb. 15, 2013

Hello, kernelnewbies There are many cases in drivers where I see calls to prefetch|() of some variable. For example, prefetch(&skb->end); in 1 bnx2_tx_int(), http://lxr.free-electrons.com/source/drivers/net/ethernet/broadcom/bnx2.c AFAIK, what prefetch does is get a variable from memory and put it in cache (L2 cache I believe). Is the prefetch operation synchronous ? I mean, after calling it, are we gauranteed that the variable is indeed in the cache ? So this is probably for improving performance, assuming that you will need this variable in the near future. The comment there says: /* prefetch skb_end_pointer() to speedup skb_shinfo(skb) */ According to this logic, anywhere that we want to call skb_shinfo(skb) we better do a prefetch before. In fact, if we prefetch any variable that we want to use then we end up with performance boost. So - any hints, what are the guidlines for using prefetch()? rgs, Kevin

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Beyond kernel-janitor
by Kumar amit mehta Feb. 15, 2013

Feb. 15, 2013

Hi All, After watching Greg's video on "How to write and submit your first patch",the discussions that happened over kernel newbie mailing list and the assorted information scattered in the kernel Documentation directory, I was able to set up my Linux box for sending janitorial related patches (mostly checkpatch.pl cleanup) [1] and I'm happy that some of those got merged in the upstream kernel I'd like to contribute even more and I was wondering how to proceed further. My work experience has been mostly in the computer network domain, so I think I've somewhat high level view of the Linux networking subsystem, but I do not know the exact areas where I should concentrate. For a beginner like me, trying to start at the core network elements is daunting. On the other hand, I do not have a networking device for which I can try to come up with a minimal device driver. Therefore In order to concentrate my work on Network subsystem of Linux, what should be the possible entry points for me. I'm planning to get myself this book [2] on Linux Network Internals. While this would take a while for me to digest all the stuff, are there any other places where I can just Jumpstart ? [1] http://marc.info/?a=135084530900004&r=1&w=2 [2] http://shop.oreilly.com/product/9780596002558.do Looking forward for your suggestions. -Amit

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(no subject)
by Kaushal Billore Feb. 15, 2013

Feb. 15, 2013

I have some doubt regarding Linux kernel V4l2 API's. When capture application calls Reqbuff ioctl to allocate n no of buffer which would belongs to v4l2 layer and display application calls the Reqbuff ioctl to allocate N no of buffer which would also belongs to device memory. Question: 1. V4l2 maintains the generic layer for all devices in which buffers can be allocated by any device and can be handle by any device? 2. If not then while capturing the data from capture device can capture device allocated buffer gets filled and while displaying the same data there memory copy happens between capture buffer and output buffers? 3. If not then I want to capture data from capture device and display onto display device through the v4l2 framework layer. Awaiting for responce! Thanks in advance Kaushal

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start address of the code segment of the program on x86-64
by Kevin Wilson Feb. 15, 2013

Feb. 15, 2013

Hi, 0×08048000 address is the start address of the code segment of a program in on x86-32. What is the start address of the code segment of the program on x86-64 ? Is there a place in the kernel code where I can add a printk on a x86_64 machine to view the code segment start ? How can it be done ? rgs Kevin

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