From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Tue, 1 Mar 2016 19:59:58 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dmitry Vyukov <dvyukov@google.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Pavel Emelyanov <xemul@parallels.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	syzkaller <syzkaller@googlegroups.com>,
	Kostya Serebryany <kcc@google.com>,
	Alexander Potapenko <glider@google.com>,
	Sasha Levin <sasha.levin@oracle.com>
Subject: Re: fs: uninterruptible hang in handle_userfault
Message-ID: <20160301195957.GD17997@ZenIV.linux.org.uk>
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On Tue, Mar 01, 2016 at 11:56:22AM -0800, Linus Torvalds wrote:
> (a) special-case the PF_EXITING case for usefaultfd, something like
> 
>     diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
>     index 50311703135b..66cdb44616d5 100644
>     --- a/fs/userfaultfd.c
>     +++ b/fs/userfaultfd.c
>     @@ -287,6 +287,12 @@ int handle_userfault(struct vm_area_struct
> *vma, unsigned long address,
>                     goto out;
> 
>             /*
>     +        * We don't do userfault handling for the final child pid update.
>     +        */
>     +       if (current->flags & PF_EXITING)
>     +               goto out;

Umm...  Probably a dumb question, but would that suffice when e.g. another
thread is just starting to dump core?