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:	Wed, 30 Mar 2016 14:46:36 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Alfredo Alvarez Fernandez <alfredoalvarezfernandez@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.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 Wed, Mar 30, 2016 at 2:43 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Mar 30, 2016 at 11:49:57AM +0200, Sedat Dilek wrote:
>> On Wed, Mar 30, 2016 at 11:36 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>
>> > OK, so while the code in check_no_collision() seems sensible, it relies
>> > on borken bits.
>> >
>> > The whole chain_hlocks and /proc/lockdep_chains stuff appears to have
>> > been buggered from the start.
>> >
>> > The below patch should fix this.
>> >
>>
>> checkpatch.pl says...
>>
>> WARNING: Prefer seq_puts to seq_printf
>> #124: FILE: kernel/locking/lockdep_proc.c:145:
>> +                       seq_printf(m, "(buggered) ");
>
> Yeah, sod checkpatch ;-)
>
> What's in your /proc/lockdep_stats file?

Eat thiz!

$ sudo cat /proc/lockdep_stats
 lock-classes:                         2012 [max: 8191]
 direct dependencies:                  9638 [max: 32768]
 indirect dependencies:               39300
 all direct dependencies:            256286
 dependency chains:                   12869 [max: 65536]
 dependency chain hlocks:             49608 [max: 327680]
 in-hardirq chains:                     115
 in-softirq chains:                     458
 in-process chains:                   11504
 stack-trace entries:                154861 [max: 524288]
 combined max dependencies:       612572220
 hardirq-safe locks:                     61
 hardirq-unsafe locks:                 1032
 softirq-safe locks:                    169
 softirq-unsafe locks:                  949
 irq-safe locks:                        178
 irq-unsafe locks:                     1032
 hardirq-read-safe locks:                 4
 hardirq-read-unsafe locks:             226
 softirq-read-safe locks:                 8
 softirq-read-unsafe locks:             221
 irq-read-safe locks:                     9
 irq-read-unsafe locks:                 226
 uncategorized locks:                   216
 unused locks:                            0
 max locking depth:                      17
 max bfs queue depth:                   354
 chain lookup misses:                 12974
 chain lookup hits:                36326533
 cyclic checks:                       11430
 find-mask forwards checks:            3952
 find-mask backwards checks:          74700
 hardirq on events:                41715052
 hardirq off events:               41715056
 redundant hardirq ons:                 404
 redundant hardirq offs:           19500606
 softirq on events:                  220687
 softirq off events:                 220715
 redundant softirq ons:                   0
 redundant softirq offs:                  0
 debug_locks:                             1

- Sedat -