Messages in this thread |  | | Date | Fri, 14 Feb 2014 15:49:07 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH] sched/core: Create new task with twice disabled preemption |
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On Fri, Feb 14, 2014 at 12:44:01PM +0000, Kirill Tkhai wrote: > В Птн, 14/02/2014 в 12:35 +0000, Catalin Marinas пишет: > > On Thu, Feb 13, 2014 at 07:51:56PM +0400, Kirill Tkhai wrote: > > > Preemption state on enter in finish_task_switch() is different > > > in cases of context_switch() and schedule_tail(). > > > > > > In the first case we have it twice disabled: at the start of > > > schedule() and during spin locking. In the second it is only > > > once: the value which was set in init_task_preempt_count(). > > > > > > For archs without __ARCH_WANT_UNLOCKED_CTXSW set this means > > > that all newly created tasks execute finish_arch_post_lock_switch() > > > and post_schedule() with preemption enabled. > > > > > > It seems there is possible a problem in rare situations on arm64, > > > when one freshly created thread preempts another before > > > finish_arch_post_lock_switch() has finished. If mm is the same, > > > then TIF_SWITCH_MM on the second won't be set. > > > > > > The second rare but possible issue is zeroing of post_schedule() > > > on a wrong cpu. > > > > > > So, lets fix this and unify preempt_count state. > > > > An alternative to your patch: > > It looks better, than the initial. > > You may add my Acked-by if you want.
Thanks for the ack. But apart from arm64, are there any other problems with running part of finish_task_switch() and post_schedule() with preemption enabled?
The finish_arch_post_lock_switch() is currently only used by arm and arm64 (the former UP only) and arm no longer has the preemption problem (see commit bdae73cd374e2). So I can either disable the preemption around schedule_tail() call in arm64 or do it globally as per yours or my patch.
Peter, Ingo, any thoughts? Do we care about preempt count consistency across finish_task_switch() and post_schedule()?
Thanks.
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