From: Andy Lutomirski <luto@amacapital.net>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Michel Lespinasse <walken@google.com>,
Hugh Dickins <hughd@google.com>, J??rn Engel <joern@logfs.org>
Subject: Re: [PATCH] mm: Downgrade mmap_sem before locking or populating on mmap
Date: Fri, 14 Dec 2012 08:12:45 -0800 [thread overview]
Message-ID: <CALCETrUS7baKF7cdbrqX-o2qdeo1Uk=7Z4MHcxHMA3Luh+Obdw@mail.gmail.com> (raw)
In-Reply-To: <20121214144927.GS4939@ZenIV.linux.org.uk>
On Fri, Dec 14, 2012 at 6:49 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Fri, Dec 14, 2012 at 03:14:50AM -0800, Andy Lutomirski wrote:
>
>> > Wait a minute. get_user_pages() relies on ->mmap_sem being held. Unless
>> > I'm seriously misreading your patch it removes that protection. And yes,
>> > I'm aware of execve-related exception; it's in special circumstances -
>> > bprm->mm is guaranteed to be not shared (and we need to rearchitect that
>> > area anyway, but that's a separate story).
>>
>> Unless I completely screwed up the patch, ->mmap_sem is still held for
>> read (it's downgraded from write). It's just not held for write
>> anymore.
>
> Huh? I'm talking about the call of get_user_pages() in aio_setup_ring().
> With your patch it's done completely outside of ->mmap_sem, isn't it?
Oh, /that/ call to get_user_pages. That would qualify as screwing up...
Since dropping and reacquiring mmap_sem there is probably a bad idea
there, I'll rework this and post a v2.
--Andy
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next prev parent reply other threads:[~2012-12-14 16:13 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-14 5:49 [PATCH] mm: Downgrade mmap_sem before locking or populating on mmap Andy Lutomirski
2012-12-14 7:27 ` Al Viro
2012-12-14 11:14 ` Andy Lutomirski
2012-12-14 14:49 ` Al Viro
2012-12-14 16:12 ` Andy Lutomirski [this message]
2012-12-16 8:41 ` Ingo Molnar
2012-12-16 17:04 ` Al Viro
2012-12-16 17:48 ` Al Viro
2012-12-16 18:49 ` Johannes Weiner
2012-12-16 19:53 ` Al Viro
2012-12-16 20:16 ` Al Viro
2012-12-15 2:17 ` [PATCH v2] " Andy Lutomirski
2012-12-16 9:00 ` Ingo Molnar
2012-12-16 17:52 ` Andy Lutomirski
2012-12-17 9:52 ` Ingo Molnar
2012-12-18 0:54 ` [PATCH v3] " Andy Lutomirski
2012-12-20 2:22 ` Simon Jeons
2012-12-16 12:39 ` [PATCH v2] " Michel Lespinasse
2012-12-16 18:05 ` Andy Lutomirski
2012-12-17 3:29 ` Michel Lespinasse
2012-12-17 22:01 ` Andy Lutomirski
2012-12-16 19:58 ` Linus Torvalds
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