On 07/11/2014 10:25 AM, Peter Zijlstra wrote:
On Thu, Jul 10, 2014 at 03:02:29PM -0400, Sasha Levin wrote:
What if we move lockdep's acquisition point to after it actually got the
lock?
NAK, you want to do deadlock detection _before_ you're stuck in a
deadlock.
We'd miss deadlocks, but we don't care about them right now. Anyways, doesn't
lockdep have anything built in to allow us to separate between locks which
we attempt to acquire and locks that are actually acquired?
(cc PeterZ)
We can treat locks that are in the process of being acquired the same as
acquired locks to avoid races, but when we print something out it would
be nice to have annotation of the read state of the lock.
I'm missing the problem here I think.
Quoting Hugh from previous mail in this thread:
>
> [ 363.600969] INFO: task trinity-c327:9203 blocked for more than 120 seconds.
> [ 363.605359] Not tainted 3.16.0-rc4-next-20140708-sasha-00022-g94c7290-dirty #772
> [ 363.609730] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 363.615861] trinity-c327 D 000000000000000b 13496 9203 8559 0x10000004
> [ 363.620284] ffff8800b857bce8 0000000000000002 ffffffff9dc11b10 0000000000000001
> [ 363.624468] ffff880104860000 ffff8800b857bfd8 00000000001d7740 00000000001d7740
> [ 363.629118] ffff880104863000 ffff880104860000 ffff8800b857bcd8 ffff8801eaed8868
> [ 363.633879] Call Trace:
> [ 363.635442] [<ffffffff9a4dc535>] schedule+0x65/0x70
> [ 363.638638] [<ffffffff9a4dc948>] schedule_preempt_disabled+0x18/0x30
> [ 363.642833] [<ffffffff9a4df0a5>] mutex_lock_nested+0x2e5/0x550
> [ 363.646599] [<ffffffff972a4d7c>] ? shmem_fallocate+0x6c/0x350
> [ 363.651319] [<ffffffff9719b721>] ? get_parent_ip+0x11/0x50
> [ 363.654683] [<ffffffff972a4d7c>] ? shmem_fallocate+0x6c/0x350
> [ 363.658264] [<ffffffff972a4d7c>] shmem_fallocate+0x6c/0x350
So it's trying to acquire i_mutex at shmem_fallocate+0x6c...
> [ 363.662010] [<ffffffff971bd96e>] ? put_lock_stats.isra.12+0xe/0x30
> [ 363.665866] [<ffffffff9730c043>] do_fallocate+0x153/0x1d0
> [ 363.669381] [<ffffffff972b472f>] SyS_madvise+0x33f/0x970
> [ 363.672906] [<ffffffff9a4e3f13>] tracesys+0xe1/0xe6
> [ 363.682900] 2 locks held by trinity-c327/9203:
> [ 363.684928] #0: (sb_writers#12){.+.+.+}, at: [<ffffffff9730c02d>] do_fallocate+0x13d/0x1d0
> [ 363.715102] #1: (&sb->s_type->i_mutex_key#16){+.+.+.}, at: [<ffffffff972a4d7c>] shmem_fallocate+0x6c/0x350
...but it already holds i_mutex, acquired at shmem_fallocate+0x6c.
Am I reading that correctly?
The output looks like mutex #1 is already taken, but actually the
process is sleeping when trying to take it. It appears that the output
has taken mutex_acquire_nest() action into account, but doesn't
distinguish if lock_acquired() already happened or not.
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