linux-kernel - Re: 4.8-rc4 spews "BUG: sleeping function called from invalid context at fs/dcache.c:757"

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Date:   Tue, 30 Aug 2016 09:55:28 +0800
From:   Ian Kent <raven@...maw.net>
To:     Al Viro <viro@...IV.linux.org.uk>, Takashi Iwai <tiwai@...e.de>
Cc:     autofs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: 4.8-rc4 spews "BUG: sleeping function called from invalid
 context at fs/dcache.c:757"

On Tue, 2016-08-30 at 09:37 +0800, Ian Kent wrote:
> On Mon, 2016-08-29 at 16:18 +0100, Al Viro wrote:
> > On Mon, Aug 29, 2016 at 04:35:46PM +0200, Takashi Iwai wrote:
> > 
> > >   [<ffffffff81260b26>] dput+0x46/0x400
> > 	... which should not be called in atomic contexts
> > >   [<ffffffff8124ff67>] follow_down_one+0x27/0x60
> > 	... and neither should this
> > >   [<ffffffff81344da2>] autofs4_mount_busy+0x32/0x110
> > 	... nor that (for fsck sake, there's full-blown path_put() in it!)
> > >   [<ffffffff81345081>] should_expire+0x51/0x3d0
> > 	... so that would better not be called in atomic either (incidentally,
> > it also calls dput() directly)
> > >   [<ffffffff81345790>] autofs4_expire_indirect+0x190/0x2d0
> > 	... while here it is called under sbi->fs_lock.
> > 
> > > I don't remember of a similar stack trace in the past, so if any, it
> > > can be a regression in 4.8 kernel.  But I cannot say it in 100%, as
> > > this looks spontaneous, nor I would be able to reproduce it at the
> > > next boot...
> > 
> > It's old; the race is narrow, but it's been there for quite a while, by
> > the look of it.
> 
> Right, I missed that when the rcu-walk concurrency changes went in, mmm ....

Umm ... no, the problem has been there much longer than that ...