Kernel Lock Debugging

[Venkatram Tummala]

On Wed, Aug 31, 2011 at 2:17 PM, Daniel Baluta <daniel.baluta at gmail.com>wrote:

> Hello,
> > i wrote a linux kernel module which uses mmap_sem in lots of places. I
> grab
> > mmap_sem for both reads & writes.  And, i also use page_table_lock
> spinlock
> > under them. The problem i have is that there is a hard to reproduce a
> race
> > condition bug in which a thread doesn't release the semaphore at all.
> Hence,
> > ps hangs as ps needs to grab mmap_sem for the processes. The question is
> how
> > do i find the thread that is holding the semaphore forever. It will help
> me
> > figure out the part of the code the race is in.
> > So, the question is : I have some number of threads grabbing the
> semaphore
> > for read/write. One of them grabs it & doesn't release at all. How do i
> find
> > the thread that is holding it. This is not a soft lockup & i dont get any
> > hung_task_timeout messages.
> > Any help is appreciated.
>
> You could turn on lockdep (LOCKDEP_SUPPORT=y),
> and see if any warnings are triggered.
>
LOCKDEP_SUPPORT is turned on in my kernel but I dont see any warnings.

Thanks though.

Venkatram

>
> thanks,
> Daniel.
>
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