On Tue, Jan 6, 2015 at 12:40 PM, Kent Overstreet <[email protected]> wrote: > On Tue, Jan 06, 2015 at 12:25:39PM +0100, Sedat Dilek wrote: >> On Tue, Jan 6, 2015 at 12:07 PM, Kent Overstreet <[email protected]> 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 <[email protected]> >> >> > 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.
I followed as far as I have understood the subsequent discussion. Let's see where this will lead to. I am also very curious about how that aio issue will be fixed. Thanks Peter and Ken for the vital and hopefully fruitful discussion. - Sedat - -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
