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From: Michal Hocko <mhocko@suse.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>, Dmitry Vyukov <dvyukov@google.com>,
	syzbot <syzbot+bfdded10ab7dcd7507ae@syzkaller.appspotmail.com>,
	Jan Kara <jack@suse.com>,
	linux-ext4@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Theodore Ts'o <tytso@mit.edu>, Linux-MM <linux-mm@kvack.org>
Subject: Re: possible deadlock in start_this_handle (2)
Date: Thu, 11 Feb 2021 15:20:41 +0100	[thread overview]
Message-ID: <YCU9OR7SfRpwl4+4@dhcp22.suse.cz> (raw)
In-Reply-To: <20210211132533.GI308988@casper.infradead.org>

On Thu 11-02-21 13:25:33, Matthew Wilcox wrote:
> On Thu, Feb 11, 2021 at 02:07:03PM +0100, Michal Hocko wrote:
> > On Thu 11-02-21 12:57:17, Matthew Wilcox wrote:
> > > > current->flags should be always manipulated from the user context. But
> > > > who knows maybe there is a bug and some interrupt handler is calling it.
> > > > This should be easy to catch no?
> > > 
> > > Why would it matter if it were?
> > 
> > I was thinking about a clobbered state because updates to ->flags are
> > not atomic because this shouldn't ever be updated concurrently. So maybe
> > a racing interrupt could corrupt the flags state?
> 
> I don't think that's possible.  Same-CPU races between interrupt and
> process context are simpler because the CPU always observes its own writes
> in order and the interrupt handler completes "between" two instructions.

I have to confess I haven't really thought the scenario through. My idea
was to simply add a simple check for an irq context into ->flags setting
routine because this should never be done in the first place. Not only
for scope gfp flags but any other PF_ flags IIRC.

-- 
Michal Hocko
SUSE Labs


  reply	other threads:[~2021-02-11 14:20 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <000000000000563a0205bafb7970@google.com>
2021-02-11 10:49 ` possible deadlock in start_this_handle (2) Jan Kara
2021-02-11 10:55   ` Michal Hocko
2021-02-11 11:22   ` Dmitry Vyukov
2021-02-11 11:28     ` Dmitry Vyukov
2021-02-11 12:10       ` Jan Kara
2021-02-11 12:34         ` Michal Hocko
2021-02-11 12:57           ` Matthew Wilcox
2021-02-11 13:07             ` Michal Hocko
2021-02-11 13:25               ` Matthew Wilcox
2021-02-11 14:20                 ` Michal Hocko [this message]
2021-02-11 14:26                   ` Matthew Wilcox
2021-02-11 16:41                     ` Michal Hocko
2021-02-12 11:18                       ` Tetsuo Handa
2021-02-12 12:22                         ` Matthew Wilcox
2021-02-12 12:30                           ` Michal Hocko
2021-02-12 12:58                             ` Tetsuo Handa
2021-02-12 13:12                               ` Michal Hocko
2021-02-12 13:34                                 ` Tetsuo Handa
2021-02-12 15:43                               ` Michal Hocko
2021-02-13 10:58                                 ` Dmitry Vyukov
2021-02-11 13:18             ` Dmitry Vyukov
2021-02-11 11:46     ` Jan Kara
2021-02-13 14:26   ` Tetsuo Handa
2021-02-15 12:45     ` Jan Kara
2021-02-15 14:06       ` Tetsuo Handa
2021-02-15 14:29         ` Jan Kara
2021-02-19 10:15           ` Tetsuo Handa
2021-02-19 17:22             ` harshad shirwadkar
2021-03-20 10:02           ` Tetsuo Handa

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