Message-ID: <s5hzj9wdygy.wl-tiwai@suse.de>
Date:	Tue, 06 Jan 2015 10:56:13 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	sedat.dilek@...il.com
Cc:	Dave Jones <davej@...emonkey.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: Linux 3.19-rc3

At Tue, 6 Jan 2015 10:34:30 +0100,
Sedat Dilek wrote:
> 
> On Tue, Jan 6, 2015 at 5:49 AM, Sedat Dilek <sedat.dilek@...il.com> wrote:
> > [ Please CC me I am not subscribed to LKML ]
> >
> > [ QUOTE ]
> >
> > On Mon, Jan 05, 2015 at 05:46:15PM -0800, Linus Torvalds wrote:
> >  > It's a day delayed - not because of any particular development issues,
> >  > but simply because I was tiling a bathroom yesterday. But rc3 is out
> >  > there now, and things have stayed reasonably calm. I really hope that
> >  > implies that 3.19 is looking good, but it's equally likely that it's
> >  > just that people are still recovering from the holiday season.
> >  >
> >  > A bit over three quarters of the changes here are drivers - mostly
> >  > networking, thermal, input layer, sound, power management. The rest is
> >  > misc - filesystems, core networking, some arch fixes, etc. But all of
> >  > it is pretty small.
> >  >
> >  > So go out and test,
> >
> > This has been there since just before rc1. Is there a fix for this
> > stalled in someones git tree maybe ?
> >
> > [    7.952588] WARNING: CPU: 0 PID: 299 at kernel/sched/core.c:7303
> > __might_sleep+0x8d/0xa0()
> > [    7.952592] do not call blocking ops when !TASK_RUNNING; state=1
> > set at [<ffffffff910a0f7a>] prepare_to_wait+0x2a/0x90
> > [    7.952595] CPU: 0 PID: 299 Comm: systemd-readahe Not tainted
> > 3.19.0-rc3+ #100
> > [    7.952597]  0000000000001c87 00000000720a2c76 ffff8800b2513c88
> > ffffffff915b47c7
> > [    7.952598]  ffffffff910a3648 ffff8800b2513ce0 ffff8800b2513cc8
> > ffffffff91062c30
> > [    7.952599]  0000000000000000 ffffffff91796fb2 000000000000026d
> > 0000000000000000
> > [    7.952600] Call Trace:
> > [    7.952603]  [<ffffffff915b47c7>] dump_stack+0x4c/0x65
> > [    7.952604]  [<ffffffff910a3648>] ? down_trylock+0x28/0x40
> > [    7.952606]  [<ffffffff91062c30>] warn_slowpath_common+0x80/0xc0
> > [    7.952607]  [<ffffffff91062cc0>] warn_slowpath_fmt+0x50/0x70
> > [    7.952608]  [<ffffffff910a0f7a>] ? prepare_to_wait+0x2a/0x90
> > [    7.952610]  [<ffffffff910a0f7a>] ? prepare_to_wait+0x2a/0x90
> > [    7.952611]  [<ffffffff910867ed>] __might_sleep+0x8d/0xa0
> > [    7.952614]  [<ffffffff915b8ea9>] mutex_lock_nested+0x39/0x3e0
> > [    7.952616]  [<ffffffff910a77ad>] ? trace_hardirqs_on+0xd/0x10
> > [    7.952617]  [<ffffffff910a0fac>] ? prepare_to_wait+0x5c/0x90
> > [    7.952620]  [<ffffffff911a63e0>] fanotify_read+0xe0/0x5b0
> > [    7.952622]  [<ffffffff91090801>] ? sched_clock_cpu+0xc1/0xd0
> > [    7.952624]  [<ffffffff91242459>] ? selinux_file_permission+0xb9/0x130
> > [    7.952626]  [<ffffffff910a14d0>] ? prepare_to_wait_event+0xf0/0xf0
> > [    7.952628]  [<ffffffff91162513>] __vfs_read+0x13/0x50
> > [    7.952629]  [<ffffffff911625d8>] vfs_read+0x88/0x140
> > [    7.952631]  [<ffffffff911626e7>] SyS_read+0x57/0xd0
> > [    7.952633]  [<ffffffff915bd952>] system_call_fastpath+0x12/0x17
> >
> > [ /QUOTE ]
> >
> > I am seeing a similiar call-trace/warning.
> > It is reproducible when running fio (latest: v2.2.4) while my loop-mq
> > tests (see block.git#for-next)
> >
> > Some people tend to say it's coming from the linux-aio area [1], but I
> > am not sure.
> > 1st I thought this is a Linux-next problem but I am seeing it also
> > with my rc-kernels.
> > For parts of aio there is a patch discussed in [2].
> > The experimental patchset of Ken from [3] made the "aio" call-trace go
> > away here.
> >
> > I tried also a patch pending in peterz/queue.git#sched/core from Eric Sandeen.
> > It's "check for stack overflow in ___might_sleep".
> > Unfortunately, it did not help in case of my loop-mq tests.
> > ( BTW, this is touching ___might_sleep() (note: triple-underscore VS.
> > affected __might_sleep() <--- double-underscrore). )
> >
> > Let me hear your feedback.
> >
> > Have more fun!
> >
> > - Sedat -
> >
> > [1] http://marc.info/?l=linux-aio&m=142033318411355&w=2
> > [2] http://marc.info/?l=linux-aio&m=142035799514685&w=2
> > [3] http://evilpiepirate.org/git/linux-bcache.git/log/?h=aio_ring_fix
> > [4] http://git.kernel.org/cgit/linux/kernel/git/peterz/queue.git/patch/?id=48e615e4c3ebed488fecb6bfb40b372151f62db2
> 
> [ CC Takashi ]
> 
> >From [1]:
> ...
> 
> Just "me too" (but overlooked until recently).
> 
> The cause is a mutex_lock() call right after prepare_to_wait() with
> TASK_INTERRUPTIBLE in fanotify_read().
> 
> static ssize_t fanotify_read(struct file *file, char __user *buf,
>     size_t count, loff_t *pos)
> {
> ....
> while (1) {
> prepare_to_wait(&group->notification_waitq, &wait, TASK_INTERRUPTIBLE);
> mutex_lock(&group->notification_mutex);
> 
> I saw Peter already fixed a similar code in inotify_user.c by commit
> e23738a7300a (but interestingly for a different reason, "Deal with
> nested sleeps").  Supposedly a similar fix would be needed for
> fanotify_user.c.
> ...
> 
> Can you explain why do you think the problem is in sched-fanotify?
> 
> I tried to do such a "similiar" (quick) fix analog to the mentioned
> "sched, inotify: Deal with nested sleeps" patch from Peter.
> If I did correct... It does not make the call-trace go away here.

Your code path is different from what Dave and I hit.  Take a closer
look at the stack trace.


Takashi
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