Blocked I/O in read() and mmap()
Le Tan
tamlokveer at gmail.com
Wed Feb 26 20:31:44 EST 2014
OK, I will look into this. Is it OK to block vm_fault?
I have another question. In my userspace program, I mmap() my device, then
read something, then munmap() my device() and then mmap() my device again.
The program do this in a loop. Everytime it mmap() the same address and
offset.
My device maintains a list of pages. In vm_operations fault, I just map the
address to the head of the list. And in vm_operations close, I just delete
the head from the list and free the page.
Everything seems to be OK except that after I call the munmap() in the
program, there is an error message. The error seems to happens between the
call of vm_operations fault and vm_operations close. I have posted this
question before ( See this<http://www.spinics.net/lists/newbies/msg51339.html>).
[42522.596689] logger_mmap():start:7f8ff57be000, end:7f8ff57bf000
//this is the mmap() function of my device module
[42522.596694]
logger_vma_fault():vmf->pgoff:0d,start:7f8ff57be000,pgoff:0,offset:0
//this is the fault function of struct vm_operations_struct
[42522.596729] BUG: Bad page map in process logger_pro
pte:8000000612a30025 pmd:314175067 //this is the error
[42522.596740] page:ffffea00184a8c00 count:2 mapcount:-2146959356
mapping: (null) index:0xffff880612a36000
[42522.596747] page flags: 0x200000000004080(slab|head)
[42522.596811] addr:00007f8ff57be000 vm_flags:04040071 anon_vma:
(null) mapping:ffff880613b25f08 index:0
[42522.596824] vma->vm_ops->fault: logger_vma_fault+0x0/0x140 [logger]
[42522.596834] vma->vm_file->f_op->mmap: logger_mmap+0x0/0xd50 [logger]
[42522.596842] CPU: 1 PID: 21571 Comm: logger_pro Tainted: G B
IO 3.11.0+ #1
[42522.596844] Hardware name: Dell Inc. PowerEdge M610/000HYJ, BIOS
2.0.13 04/06/2010
[42522.596846] 00007f8ff57be000 ffff880314199c98 ffffffff816ad166
0000000000006959
[42522.596851] ffff880314539a98 ffff880314199ce8 ffffffff8114e270
ffffea00184a8c00
[42522.596854] 0000000000000000 ffff880314199cc8 00007f8ff57be000
ffff880314199e18
[42522.596858] Call Trace:
[42522.596867] [<ffffffff816ad166>] dump_stack+0x46/0x58
[42522.596872] [<ffffffff8114e270>] print_bad_pte+0x190/0x250
[42522.596877] [<ffffffff8115027b>] unmap_single_vma+0x6cb/0x7a0
[42522.596880] [<ffffffff81150bd4>] unmap_vmas+0x54/0xa0
[42522.596885] [<ffffffff81155aa7>] unmap_region+0xa7/0x110
[42522.596888] [<ffffffff81157f97>] do_munmap+0x1f7/0x3e0
[42522.596891] [<ffffffff811581ce>] vm_munmap+0x4e/0x70
[42522.596904] [<ffffffff811591bb>] SyS_munmap+0x2b/0x40
[42522.596915] [<ffffffff816bc9c2>] system_call_fastpath+0x16/0x1b
[42522.596920] logger_vma_close():start:7f8ff57be000,
end:7f8ff57bf000, vmas:0 //this is the close function of struct
vm_operations_struct
So do you have any idea about this error?
Thanks very much!
2014-02-27 9:04 GMT+08:00 Rajat Sharma <fs.rajat at gmail.com>:
> Why do you need to block in mmap()? mmap is supposed to create a mapping
> area in virtual address space for the process. Actual transfer happens
> later through page fault handlers on demand basis. look at vm_operations
> fault/readpage etc methods, these might be the places you want to wait for
> the data.
>
>
> On Wed, Feb 26, 2014 at 4:14 PM, Le Tan <tamlokveer at gmail.com> wrote:
>
>> So what should I do if I want the mmap() not to return right now? Is
>> it strange to block in mmap() and few people will do this? Thanks for
>> your help!
>>
>> 2014-02-27 4:45 GMT+08:00 Rajat Sharma <fs.rajat at gmail.com>:
>> > It seems this task "landscape-sysin" is trying to peek into virtual
>> memory
>> > of your processes and the process within mmap call is holding its
>> > mm->mmap_sem semaphore which grants access to its address space.
>> > landscape-sysin is trying to grab this semaphore to poke into address
>> space
>> > of your mmap process address space. As from your description, it might
>> be
>> > invoked everytime you are opening a new shell. Not sure why this process
>> > bother's about other process address space. Little googling shows this
>> as
>> > relevant to your case:
>> >
>> >
>> http://www.techques.com/question/2-66765/Disable-usage-of-console-kit-daemon-in-Ubuntu
>> >
>> > Your read process is innocent and not involved in this deadlock.
>> >
>> > -Rajat
>> >
>> >
>> > On Wed, Feb 26, 2014 at 4:13 AM, Le Tan <tamlokveer at gmail.com> wrote:
>> >>
>> >> Hi, I am writing a driver module. Now I have some questions about
>> blocked
>> >> I/O.
>> >> my_read() is the read function in the file_operations struct in my
>> >> module. my_read() is just as simple as this:
>> >> ssize_t my_read(....)
>> >> {
>> >> if(wait_event_interruptible(dev->queue, a == b))
>> >> return -ERESTARTSYS;
>> >> return count;
>> >> }
>> >> Then I write a simple program to open and read the device. Obviously
>> >> the program will be blocked. Now I still can open a new shell window
>> >> and log in ( I use xshell).
>> >>
>> >> However, then I implement my_mmap(), the mmap function in the
>> >> file_operations struct in my module, like this:
>> >> int my_mmap(....)
>> >> {
>> >> if(wait_event_interruptible(dev->queue, a == b))
>> >> return -ERESTARTSYS;
>> >> return 0;
>> >> }
>> >> Then I write a simple program to open and mmap() the device. Obviously
>> >> the program will be blocked again. However, when I open a new shell
>> >> window in xshell and try to connect to the linux, it displays like
>> >> this:
>> >>
>> >> Connecting to 192.168.146.118:22...
>> >> Connection established.
>> >> To escape to local shell, press 'Ctrl+Alt+]'.
>> >>
>> >> And I can't log in! Then after a while, in the syslog, there is one
>> >> message like this:
>> >> [38306.614103] INFO: task landscape-sysin:17616 blocked for more than
>> >> 120 seconds.
>> >> [38306.614114] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
>> >> disables this message.
>> >> [38306.614120] landscape-sysin D ffffffff8180fb60 0 17616 17609
>> >> 0x00000000
>> >> [38306.614125] ffff88031d609c90 0000000000000082 ffff88032fffdb08
>> >> 0000000000000000
>> >> [38306.614130] ffff8803130bdc40 ffff88031d609fd8 ffff88031d609fd8
>> >> ffff88031d609fd8
>> >> [38306.614133] ffff88062150c530 ffff8803130bdc40 0000004100000000
>> >> ffff8803130bdc40
>> >> [38306.614137] Call Trace:
>> >> [38306.614147] [<ffffffff816b2c49>] schedule+0x29/0x70
>> >> [38306.614151] [<ffffffff816b3acd>] rwsem_down_read_failed+0x9d/0xf0
>> >> [38306.614157] [<ffffffff81341824>]
>> call_rwsem_down_read_failed+0x14/0x30
>> >> [38306.614160] [<ffffffff816b1644>] ? down_read+0x24/0x2b
>> >> [38306.614166] [<ffffffff81153661>] __access_remote_vm+0x41/0x1f0
>> >> [38306.614170] [<ffffffff81153ddb>] access_process_vm+0x5b/0x80
>> >> [38306.614175] [<ffffffff811ea423>] proc_pid_cmdline+0x93/0x120
>> >> [38306.614178] [<ffffffff811eb425>] proc_info_read+0xa5/0xf0
>> >> [38306.614182] [<ffffffff81186e84>] vfs_read+0xb4/0x180
>> >> [38306.614185] [<ffffffff81187102>] SyS_read+0x52/0xa0
>> >> [38306.614189] [<ffffffff816bc8c2>] system_call_fastpath+0x16/0x1b
>> >>
>> >> If I terminate the program by force, then I can log in right now.
>> >> So, are there any differences between the read and the mmap function
>> >> to the wait_event_interruptible()? Why? If I want to block mmap() just
>> >> like blocking read(), what should I do? Or it is impossible?
>> >> Thanks!
>> >>
>> >> _______________________________________________
>> >> Kernelnewbies mailing list
>> >> Kernelnewbies at kernelnewbies.org
>> >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>> >
>> >
>>
>
>
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