linux-kernel - Re: proc_flush

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Message-ID: <20171221031606.GA4636@codemonkey.org.uk>
Date:   Wed, 20 Dec 2017 22:16:06 -0500
From:   Dave Jones <davej@...emonkey.org.uk>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com, Gargi Sharma <gs051095@...il.com>,
        Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: proc_flush_task oops

On Wed, Dec 20, 2017 at 12:25:52PM -0600, Eric W. Biederman wrote:
> >  > 
 > >  > If the warning triggers it means the bug is in alloc_pid and somehow
 > >  > something has gotten past the is_child_reaper check.
 > >
 > > You're onto something.
 > >
 > I am not seeing where things go wrong, but that puts the recent pid bitmap, bit
 > hash to idr change in the suspect zone.
 > 
 > Can you try reverting that change:
 > 
 > e8cfbc245e24 ("pid: remove pidhash")
 > 95846ecf9dac ("pid: replace pid bitmap implementation with IDR API")
 > 
 > While keeping the warning in place so we can see if this fixes the
 > allocation problem?

So I can't trigger this any more with those reverted.  I seem to hit a
bunch of other long-standing bugs first.  I'll keep running it
overnight, but it looks like this is where the problem lies.

	Dave