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SubjectRe: [locking/ww_mutex] 857811a371 BUG: kernel hang in boot stage
On Tue, Mar 28, 2017 at 05:07:09PM +0800, Fengguang Wu wrote:
> Greetings,
>
> 0day kernel testing robot got the below dmesg and the first bad commit is
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>
> commit 857811a37129f5d2ba162d7be3986eff44724014
> Author: Boqun Feng <boqun.feng@gmail.com>
> AuthorDate: Wed Mar 1 23:01:38 2017 +0800
> Commit: Ingo Molnar <mingo@kernel.org>
> CommitDate: Thu Mar 2 09:00:39 2017 +0100
>
> locking/ww_mutex: Adjust the lock number for stress test
>
> Because there are only 12 bits in held_lock::references, so we only
> support 4095 nested lock held in the same time, adjust the lock number
> for ww_mutex stress test to kill one lockdep splat:
>
> [ ] [ BUG: bad unlock balance detected! ]
> [ ] kworker/u2:0/5 is trying to release lock (ww_class_mutex) at:
> [ ] ww_mutex_unlock()
> [ ] but there are no more locks to release!
> ...
>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Fengguang Wu <fengguang.wu@intel.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Link: http://lkml.kernel.org/r/20170301150138.hdixnmafzfsox7nn@tardis.cn.ibm.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
>
> 7fb4a2cea6 locking/lockdep: Add nest_lock integrity test
> 857811a371 locking/ww_mutex: Adjust the lock number for stress test
> c02ed2e75e Linux 4.11-rc4
> 7f0c4a163a Add linux-next specific files for 20170327
> +-----------------------------------------------------+------------+------------+-----------+---------------+
> | | 7fb4a2cea6 | 857811a371 | v4.11-rc4 | next-20170327 |
> +-----------------------------------------------------+------------+------------+-----------+---------------+
> | boot_successes | 0 | 16 | 29 | 1 |
> | boot_failures | 221 | 42 | 64 | 9 |
> | WARNING:at_kernel/locking/lockdep.c:#__lock_acquire | 221 | | | |
> | BUG:kernel_hang_in_boot_stage | 0 | 42 | 60 | 9 |
> | BUG:kernel_hang_in_test_stage | 0 | 0 | 4 | |
> +-----------------------------------------------------+------------+------------+-----------+---------------+
>
> [ 319.426004] CPU 0 is now offline
> [ 319.426004] CPU 0 is now offline
> [ 319.427670]
> <kernel hangs here>
>

Hmm.. with the same reproduce script, I'm able to reproduce the hang
even with CONIFG_WW_MUTEX_SELFTEST=N. Fengguang, could you try to verify
whether ww_mutex test is related to this hang?

Regards,
Boqun
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