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Date: Wed, 3 Aug 2016 11:56:16 -0700 From: Bart Van Assche <bart.vanassche@...disk.com> To: Peter Zijlstra <peterz@...radead.org> CC: "mingo@...nel.org" <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, Neil Brown <neilb@...e.de>, Michael Shaver <jmshaver@...il.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Oleg Nesterov <oleg@...hat.com> Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs On 08/03/2016 11:11 AM, Peter Zijlstra wrote: > That seems to do the right thing, so clearly I misunderstand. Please > clarify. Hello Peter, try_to_wake_up() locks task_struct.pi_lock but abort_exclusive_wait() not. My assumption is that the following sequence of events leads to the lockup that I had mentioned in the description of my patch: * try_to_wake_up() is called for the task that will execute abort_exclusive_wait(). * After try_to_wake_up() has checked task_struct.state and before autoremove_wake_function() has tried to remove the task from the wait queue, abort_exclusive_wait() is executed for the same task. Please note that the call stack I had mentioned in my e-mail had been reported before. See e.g. * Michael Shaver, Kernel deadlock during mdadm reshape, July 2016 (http://www.spinics.net/lists/raid/msg53056.html). * Bart Van Assche, Kernel hangs in truncate_inode_pages(), August 2012 (https://lkml.org/lkml/2012/8/24/185). Bart.
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