linux-kernel - Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at kernel/locking/lockdep.c:2017 __lock

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Date:	Sun, 27 Mar 2016 22:59:00 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Theodore Ts'o" <tytso@....edu>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-v4.6-rc1] ext4: WARNING: CPU: 2 PID: 2692 at
 kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260

On Sun, Mar 27, 2016 at 10:48 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Sun, Mar 27, 2016 at 05:03:44AM -0700, Linus Torvalds wrote:
>> Anyway, I don't think that DEBUG_LOCKS_WARN_ON() in
>>
>>   kernel/locking/lockdep.c:2017 __lock_acquire
>>
>> would be an ext4 issue, it looks more like an internal lockdep issue.
>>
>> Adding in the lockdep people, who will set me right.
>
> You are right; this is lockdep running into a hash collision; which is a
> new DEBUG_LOCKDEP test. See 9e4e7554e755 ("locking/lockdep: Detect
> chain_key collisions").

[1] says...

"Also tested with lockdep's test suite after applying the patch:

[ 0.000000] Good, all 253 testcases passed! |"

Where can I find this "lockdep's test suite"?

When is that checking below done or what causes this?

$ grep -i lock dmesg_4.6.0-rc1-1-iniza-small.txt | grep -i dep
[    0.000000]  RCU lockdep checking is enabled.
[    0.000000] Lock dependency validator: Copyright (c) 2006 Red Hat,
Inc., Ingo Molnar
[    0.000000] ... MAX_LOCKDEP_SUBCLASSES:  8
[    0.000000] ... MAX_LOCK_DEPTH:          48
[    0.000000] ... MAX_LOCKDEP_KEYS:        8191
[    0.000000] ... MAX_LOCKDEP_ENTRIES:     32768
[    0.000000] ... MAX_LOCKDEP_CHAINS:      65536
[    0.000000]  memory used by lock dependency info: 8159 kB
[   77.403391] WARNING: CPU: 2 PID: 2692 at
kernel/locking/lockdep.c:2017 __lock_acquire+0x180e/0x2260
[   77.403394] DEBUG_LOCKS_WARN_ON(chain->depth != curr->lockdep_depth
- (i - 1))

- Sedat -

[1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=9e4e7554e755

View attachment "dmesg_4.6.0-rc1-1-iniza-small.txt" of type "text/plain" (58066 bytes)