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Message-ID: <20150106114056.GB25846@kmo-pixel> Date: Tue, 6 Jan 2015 03:40:56 -0800 From: Kent Overstreet <kmo@...erainc.com> To: Sedat Dilek <sedat.dilek@...il.com> Cc: Peter Zijlstra <peterz@...radead.org>, Dave Jones <davej@...emonkey.org.uk>, Linus Torvalds <torvalds@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org>, Chris Mason <clm@...com> Subject: Re: Linux 3.19-rc3 On Tue, Jan 06, 2015 at 12:25:39PM +0100, Sedat Dilek wrote: > On Tue, Jan 6, 2015 at 12:07 PM, Kent Overstreet <kmo@...erainc.com> wrote: > > On Tue, Jan 06, 2015 at 12:01:12PM +0100, Peter Zijlstra wrote: > >> On Tue, Jan 06, 2015 at 11:18:04AM +0100, Sedat Dilek wrote: > >> > On Tue, Jan 6, 2015 at 11:06 AM, Peter Zijlstra <peterz@...radead.org> wrote: > >> > > On Tue, Jan 06, 2015 at 10:57:19AM +0100, Sedat Dilek wrote: > >> > >> [ 88.028739] [<ffffffff8124433f>] aio_read_events+0x4f/0x2d0 > >> > >> > >> > > > >> > > Ah, that one. Chris Mason and Kent Overstreet were looking at that one. > >> > > I'm not touching the AIO code either ;-) > >> > > >> > I know, I was so excited when I see nearly the same output. > >> > > >> > Can you tell me why people see "similiar" problems in different areas? > >> > >> Because the debug check is new :-) It's a pattern that should not be > >> used but mostly works most of the times. > >> > >> > [ 181.397024] WARNING: CPU: 0 PID: 2872 at kernel/sched/core.c:7303 > >> > __might_sleep+0xbd/0xd0() > >> > [ 181.397028] do not call blocking ops when !TASK_RUNNING; state=1 > >> > set at [<ffffffff810b83bd>] prepare_to_wait_event+0x5d/0x110 > >> > > >> > With similiar buzzwords... namely... > >> > > >> > mutex_lock_nested > >> > prepare_to_wait(_event) > >> > __might_sleep > >> > > >> > I am asking myself... Where is the real root cause - in sched/core? > >> > Fix one single place VS. fix the impact at several other places? > >> > >> No, the root cause is nesting sleep primitives, this is not fixable in > >> the one place, both prepare_to_wait and mutex_lock are using > >> task_struct::state, they have to, no way around it. > > > > No, it's completely possible to construct a prepare_to_wait() that doesn't > > require messing with the task state. Had it for years. > > > > http://evilpiepirate.org/git/linux-bcache.git/log/?h=aio_ring_fix > > I am just rebuilding a new kernel with "aio_ring_fix" included - I > have tested this alread with loop-mq and it made the call-trace in aio > go away. > > > Jut curious... > How would a patch look like a patch to fix the sched-fanotify issue > with a conversion to "closure waitlist"? wait_queue_head_t -> struct closure_waitlist DEFINE_WAIT() -> struct closure cl; closure_init_stack(&cl) prepare_to_wait() -> closure_wait(&waitlist, &cl) schedule() -> closure_sync() finish_wait() -> closure_wake_up(); closure_sync() That's the standard conversion, I haven't looked at the fanotify code before just now but from a cursory glance it appears that all should work here. Only annoying thing is the waitqueue here is actually part of the poll interface (if I'm reading this correctly), so I dunno what I'd do about that. Also FYI: closure waitlists are currently singly linked, thus there's no direct equivalent to finish_wait(), the conversion I gave works but will lead to spurious wakeups. I kinda figured I was going to have to switch to doubly linked lists eventually though. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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