linux-kernel - Re: [BUG] perf_event: circular lock dependency

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Date:	Thu, 28 Jan 2010 10:48:17 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [BUG] perf_event: circular lock dependency

On Thu, Jan 28, 2010 at 10:32 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2010-01-28 at 10:19 +0100, Stephane Eranian wrote:
>
>> On Intel Core, one of my test programs generate this kind of
>> warning when it unmaps the sampling buffer after it has closed
>> the events fds.
>
>> [ 1729.441066] the existing dependency chain (in reverse order) is:
>> [ 1729.441092]
>> [ 1729.441093] -> #1 (&mm->mmap_sem){++++++}:
>> [ 1729.441123]        [<ffffffff81077f97>] validate_chain+0xc17/0x1360
>> [ 1729.441151]        [<ffffffff81078a53>] __lock_acquire+0x373/0xb30
>> [ 1729.441170]        [<ffffffff810792ac>] lock_acquire+0x9c/0x100
>> [ 1729.441189]        [<ffffffff810e74a4>] might_fault+0x84/0xb0
>> [ 1729.441207]        [<ffffffff810c3605>] perf_read+0x135/0x2d0
>> [ 1729.441225]        [<ffffffff8110c604>] vfs_read+0xc4/0x180
>> [ 1729.441245]        [<ffffffff8110ca10>] sys_read+0x50/0x90
>> [ 1729.441263]        [<ffffffff81002ceb>] system_call_fastpath+0x16/0x1b
>> [ 1729.441284]
>> [ 1729.441284] -> #0 (&ctx->mutex){+.+...}:
>> [ 1729.441313]        [<ffffffff810786cd>] validate_chain+0x134d/0x1360
>> [ 1729.441332]        [<ffffffff81078a53>] __lock_acquire+0x373/0xb30
>> [ 1729.441351]        [<ffffffff810792ac>] lock_acquire+0x9c/0x100
>> [ 1729.441369]        [<ffffffff81442e59>] mutex_lock_nested+0x69/0x340
>> [ 1729.441389]        [<ffffffff810c2ebd>] perf_event_release_kernel+0x2d/0xe0
>> [ 1729.441409]        [<ffffffff810c2f8b>] perf_release+0x1b/0x20
>> [ 1729.441426]        [<ffffffff8110d051>] __fput+0x101/0x230
>> [ 1729.441444]        [<ffffffff8110d457>] fput+0x17/0x20
>> [ 1729.441462]        [<ffffffff810e98d1>] remove_vma+0x51/0x90
>> [ 1729.441480]        [<ffffffff810ea708>] do_munmap+0x2e8/0x340
>> [ 1729.441498]        [<ffffffff810ebac0>] sys_munmap+0x50/0x80
>> [ 1729.441516]        [<ffffffff81002ceb>] system_call_fastpath+0x16/0x1b
>> [ 1729.441535]
>
> Crap, the thing is right.. you've been using group reads, which require
> holding the ctx->mutex to ensure the group doesn't change while you're
> reading it, leading to this inversion thing...
>
Correct, I am using PERF_READ_GROUP and PERF_SAMPLE_READ.

> Not sure where to break this loop though, the hacky way is pushing all
> of perf_event_release_kernel() into a work, but that's yucky.. Let me
> ponder this a bit more.
>
>



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