From: ebiederm@xmission.com (Eric W. Biederman)
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Hugh Dickins <hugh@veritas.com>,
Al Viro <viro@ZenIV.linux.org.uk>,
Alexey Dobriyan <adobriyan@gmail.com>,
akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: 2.6.27-rc7-sha1: EIP at proc_sys_compare+0x36/0x50
Date: Sun, 28 Sep 2008 20:05:22 -0700 [thread overview]
Message-ID: <m1hc7zabyl.fsf@frodo.ebiederm.org> (raw)
In-Reply-To: <alpine.LFD.1.10.0809281350410.3265@nehalem.linux-foundation.org> (Linus Torvalds's message of "Sun, 28 Sep 2008 13:55:29 -0700 (PDT)")
Linus Torvalds <torvalds@linux-foundation.org> writes:
> I actually like my second patch better - it looks simpler, and it means
> that the rules for filesystems using d_compare() are a bit clearer: at
> least we'll only pass them dentries to look at that haven't gone through
> d_drop (and we do hold dentry->d_lock that serializes all of that).
>
> So here it is again (I sent it out just minutes ago, but you weren't on
> that cc, you must have picked this up off the kernel list)
>
> NOTE! Totally untested patch! It looks sane and really obvious, but maybe
> it has some insane and non-obvious bug.
We definitely have a race between d_kill setting dentry->d_inode = NULL
and proc_sys_compare reading d_inode.
We don't generate negative dentries for /proc/sys.
In dput atomic_dec_and_lock takes the lock before setting the count to 0.
So there is no race there.
Testing for d_unhashed and getting us out of rcu limbo before calling
into the filesystem methods makes the reasoning a lot clearer.
Looks good to me.
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
next prev parent reply other threads:[~2008-09-29 3:05 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-09-26 15:20 2.6.27-rc7-sha1: EIP at proc_sys_compare+0x36/0x50 Alexey Dobriyan
2008-09-26 15:47 ` Linus Torvalds
2008-09-27 8:44 ` Eric W. Biederman
2008-09-28 20:38 ` Linus Torvalds
2008-09-28 14:18 ` Al Viro
2008-09-28 19:28 ` Hugh Dickins
2008-09-28 20:55 ` Linus Torvalds
2008-09-28 20:59 ` Linus Torvalds
2008-09-28 22:07 ` Hugh Dickins
2008-09-29 3:05 ` Eric W. Biederman [this message]
2008-09-28 20:46 ` Linus Torvalds
2008-09-28 20:50 ` Linus Torvalds
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