Re: rcu: BUG on exit_group

[Paul E. McKenney]

On Thu, May 03, 2012 at 10:57:19AM +0200, Sasha Levin wrote:
> Hi Paul,
> 
> I've hit a BUG similar to the schedule_tail() one when. It happened
> when I've started fuzzing exit_group() syscalls, and all of the traces
> are starting with exit_group() (there's a flood of them).
> 
> I've verified that it indeed BUGs due to the rcu preempt count.

Hello, Sasha,

Which version of -next are you using?  I did some surgery on this
yesterday based on some bugs Hugh Dickins tracked down, so if you
are using something older, please move to the current -next.

						Thanx, Paul

> Here's one of the BUG()s:
> 
> [   83.820976] BUG: sleeping function called from invalid context at
> kernel/mutex.c:269
> [   83.827870] in_atomic(): 0, irqs_disabled(): 0, pid: 4506, name: trinity
> [   83.832154] 1 lock held by trinity/4506:
> [   83.834224]  #0:  (rcu_read_lock){.+.+..}, at: [<ffffffff811a7d87>]
> munlock_vma_page+0x197/0x200
> [   83.839310] Pid: 4506, comm: trinity Tainted: G        W
> 3.4.0-rc5-next-20120503-sasha-00002-g09f55ae-dirty #108
> [   83.849418] Call Trace:
> [   83.851182]  [<ffffffff810e7218>] __might_sleep+0x1f8/0x210
> [   83.854076]  [<ffffffff82d9540a>] mutex_lock_nested+0x2a/0x50
> [   83.857120]  [<ffffffff811b0830>] try_to_unmap_file+0x40/0x2f0
> [   83.860242]  [<ffffffff82d984bb>] ? _raw_spin_unlock_irq+0x2b/0x80
> [   83.863423]  [<ffffffff810e7ffe>] ? sub_preempt_count+0xae/0xf0
> [   83.866347]  [<ffffffff82d984e9>] ? _raw_spin_unlock_irq+0x59/0x80
> [   83.869570]  [<ffffffff811b0caa>] try_to_munlock+0x6a/0x80
> [   83.872667]  [<ffffffff811a7cc6>] munlock_vma_page+0xd6/0x200
> [   83.875646]  [<ffffffff811a7d87>] ? munlock_vma_page+0x197/0x200
> [   83.878798]  [<ffffffff811a7e7f>] munlock_vma_pages_range+0x8f/0xd0
> [   83.882235]  [<ffffffff811a8b8a>] exit_mmap+0x5a/0x160
> [   83.884880]  [<ffffffff810ba23b>] ? exit_mm+0x10b/0x130
> [   83.887508]  [<ffffffff8111d8ea>] ? __lock_release+0x1ba/0x1d0
> [   83.890399]  [<ffffffff810b4fe1>] mmput+0x81/0xe0
> [   83.892966]  [<ffffffff810ba24b>] exit_mm+0x11b/0x130
> [   83.895640]  [<ffffffff82d984e9>] ? _raw_spin_unlock_irq+0x59/0x80
> [   83.898943]  [<ffffffff810bca53>] do_exit+0x263/0x460
> [   83.901700]  [<ffffffff810bccf1>] do_group_exit+0xa1/0xe0
> [   83.907366]  [<ffffffff810bcd42>] sys_exit_group+0x12/0x20
> [   83.912450]  [<ffffffff82d993b9>] system_call_fastpath+0x16/0x1b
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