From: Davidlohr Bueso <davidlohr.bueso@hp.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Emmanuel Benisty <benisty.e@gmail.com>,
Dave Jones <davej@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@surriel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
hhuang@redhat.com, "Low, Jason" <jason.low2@hp.com>,
Michel Lespinasse <walken@google.com>,
Larry Woodman <lwoodman@redhat.com>,
"Vinod, Chegu" <chegu_vinod@hp.com>,
Peter Hurley <peter@hurleysoftware.com>
Subject: Re: ipc,sem: sysv semaphore scalability
Date: Fri, 29 Mar 2013 19:55:06 -0700 [thread overview]
Message-ID: <1364612106.1818.14.camel@buesod1.americas.hpqcorp.net> (raw)
In-Reply-To: <CA+55aFyksNnZJTL2WSV87s2CUBXouF9KVxDddYp9r1radBfFAA@mail.gmail.com>
On Fri, 2013-03-29 at 19:09 -0700, Linus Torvalds wrote:
> On Fri, Mar 29, 2013 at 6:36 PM, Emmanuel Benisty <benisty.e@gmail.com> wrote:
> >
> > I had to slightly modify the patch since it wouldn't match the changes
> > introduced by 7-7-ipc-sem-fine-grained-locking-for-semtimedop.patch,
> > hope that was the right thing to do. So, what I tried was: original 7
> > patches + the one liner + your patch blindly modified by me on the top
> > of 3.9-rc4 and I'm still having twilight zone issues.
>
> Ok, please send your patch so that I can double-check what you did,
> but it was simple enough that you probably did the right thing.
>
> Sad. Your case definitely looks like a double rcu-free, as shown by
> the fact that when you enabled SLUB debugging the oops happened with
> the use-after-free pattern (it's __rcu_reclaim() doing the
> "head->func(head);" thing, and "func" is 0x6b6b6b6b6b6b6b6b, so "head"
> has already been free'd once).
>
> So ipc_rcu_putref() and a refcounting error looked very promising.as a
> potential explanation.
>
> The 'un' undo structure is also free'd with rcu, but the locking
> around that seems much more robust. The undo entry is on two lists
> (sma->list_id, under sma->sem_perm.lock and ulp->list_proc, under
> ulp->lock). But those locks are actually tested with
> assert_spin_locked() in all the relevant places, and the code actually
> looks sane. So I had high hopes for ipc_rcu_putref()...
>
> Hmm. Except for exit_sem() that does odd things. You have preemption
> enabled, don't you? exit_sem() does a lookup of the first list_proc
> entry under tcy_read_lock to lookup un->semid, and then it drops the
> rcu read lock. At which point "un" is no longer reliable, I think. But
> then it still uses "un->semid", rather than the stable value it looked
> up under the rcu read lock. Which looks bogus.
>
> So I'd like you to test a few more things:
>
> (a) In exit_sem(), can you change the
>
> sma = sem_lock_check(tsk->nsproxy->ipc_ns, un->semid);
>
> to use just "semid" rather than "un->semid", because I don't
> think "un" is stable here.
Well that's not really the case in the new code. We don't drop the rcu
read lock until the end of the loop, in sem_unlock(). However, I just
noticed that we're checking sma for error after trying to acquire
sma->sem_perm.lock:
sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, un->semid);
sem_lock(sma, NULL, -1);
/* exit_sem raced with IPC_RMID, nothing to do */
if (IS_ERR(sma))
continue;
The IS_ERR(sma) check should be right after the sem_obtain_object_check() call instead.
next prev parent reply other threads:[~2013-03-30 2:55 UTC|newest]
Thread overview: 129+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-20 19:55 ipc,sem: sysv semaphore scalability Rik van Riel
2013-03-20 19:55 ` [PATCH 1/7] ipc: remove bogus lock comment for ipc_checkid Rik van Riel
2013-03-20 19:55 ` [PATCH 2/7] ipc: introduce obtaining a lockless ipc object Rik van Riel
2013-03-20 19:55 ` [PATCH 3/7] ipc: introduce lockless pre_down ipcctl Rik van Riel
2013-03-20 19:55 ` [PATCH 4/7] ipc,sem: do not hold ipc lock more than necessary Rik van Riel
2013-03-20 19:55 ` [PATCH 5/7] ipc,sem: open code and rename sem_lock Rik van Riel
2013-03-22 1:14 ` Davidlohr Bueso
2013-03-20 19:55 ` [PATCH 6/7] ipc,sem: have only one list in struct sem_queue Rik van Riel
2013-03-22 1:14 ` Davidlohr Bueso
2013-03-20 19:55 ` [PATCH 7/7] ipc,sem: fine grained locking for semtimedop Rik van Riel
2013-03-22 1:14 ` Davidlohr Bueso
2013-03-22 23:01 ` Michel Lespinasse
2013-03-22 23:38 ` Rik van Riel
2013-03-22 23:42 ` [PATCH 7/7 part3] fix for sem_lock Rik van Riel
2013-03-20 20:49 ` ipc,sem: sysv semaphore scalability Linus Torvalds
2013-03-20 20:56 ` Linus Torvalds
2013-03-20 20:57 ` Davidlohr Bueso
2013-03-21 21:10 ` Andrew Morton
2013-03-21 21:47 ` Peter Hurley
2013-03-21 21:50 ` Peter Hurley
2013-03-21 22:01 ` Andrew Morton
2013-03-22 3:38 ` Rik van Riel
2013-03-26 19:28 ` Dave Jones
2013-03-26 19:43 ` Andrew Morton
2013-03-29 16:17 ` Dave Jones
2013-03-29 18:00 ` Linus Torvalds
2013-03-29 18:04 ` Dave Jones
2013-03-29 18:10 ` Linus Torvalds
2013-03-29 18:43 ` Linus Torvalds
2013-03-29 19:06 ` Dave Jones
2013-03-29 19:13 ` Linus Torvalds
2013-03-29 19:26 ` Linus Torvalds
2013-03-29 19:36 ` Peter Hurley
2013-04-02 16:08 ` Sasha Levin
2013-04-02 17:24 ` Linus Torvalds
2013-04-02 17:52 ` Linus Torvalds
2013-04-02 19:53 ` Sasha Levin
2013-04-02 20:00 ` Dave Jones
2013-03-29 19:33 ` Peter Hurley
2013-03-29 19:54 ` Linus Torvalds
2013-04-01 7:40 ` Stanislav Kinsbursky
2013-03-29 20:41 ` Linus Torvalds
2013-03-29 21:12 ` Linus Torvalds
2013-03-29 23:16 ` Linus Torvalds
2013-03-30 1:36 ` Emmanuel Benisty
2013-03-30 2:08 ` Davidlohr Bueso
2013-03-30 3:02 ` Emmanuel Benisty
2013-03-30 3:46 ` Linus Torvalds
2013-03-30 4:33 ` Emmanuel Benisty
2013-03-30 5:10 ` Linus Torvalds
2013-03-30 5:57 ` Emmanuel Benisty
2013-03-30 17:22 ` Linus Torvalds
2013-03-31 2:38 ` Emmanuel Benisty
2013-03-31 5:01 ` Davidlohr Bueso
2013-03-31 13:45 ` Rik van Riel
2013-03-31 17:10 ` Linus Torvalds
2013-03-31 17:02 ` Emmanuel Benisty
2013-03-30 2:09 ` Linus Torvalds
2013-03-30 2:55 ` Davidlohr Bueso [this message]
2013-03-29 19:01 ` Dave Jones
2013-05-03 15:03 ` Peter Hurley
2013-03-22 1:12 ` Davidlohr Bueso
2013-03-22 1:23 ` Linus Torvalds
2013-03-22 3:40 ` Rik van Riel
2013-03-22 7:30 ` Mike Galbraith
2013-03-22 11:04 ` Emmanuel Benisty
2013-03-22 15:37 ` Linus Torvalds
2013-03-23 3:19 ` Emmanuel Benisty
2013-03-23 19:45 ` Linus Torvalds
2013-03-24 13:46 ` Emmanuel Benisty
2013-03-24 17:10 ` Linus Torvalds
2013-03-25 13:47 ` Emmanuel Benisty
2013-03-25 14:00 ` Rik van Riel
2013-03-25 14:03 ` Rik van Riel
2013-03-25 15:20 ` Emmanuel Benisty
2013-03-25 15:53 ` Rik van Riel
2013-03-25 17:09 ` Emmanuel Benisty
2013-03-25 14:01 ` Rik van Riel
2013-03-25 14:21 ` Emmanuel Benisty
2013-03-26 17:59 ` Davidlohr Bueso
2013-03-26 18:14 ` Rik van Riel
2013-03-26 18:35 ` Andrew Morton
2013-04-16 23:30 ` Andrew Morton
2013-05-04 15:55 ` Jörn Engel
2013-05-04 18:12 ` Borislav Petkov
2013-05-06 14:47 ` Jörn Engel
2013-03-22 17:51 ` Davidlohr Bueso
2013-03-25 20:21 ` Sasha Levin
2013-03-25 20:38 ` [PATCH -mm -next] ipc,sem: fix lockdep false positive Rik van Riel
2013-03-25 21:42 ` Michel Lespinasse
2013-03-25 21:51 ` Michel Lespinasse
2013-03-25 21:56 ` Sasha Levin
2013-03-25 21:52 ` Sasha Levin
2013-03-26 13:19 ` Peter Zijlstra
2013-03-26 13:40 ` Michel Lespinasse
2013-03-26 14:27 ` Peter Zijlstra
2013-03-26 15:19 ` Rik van Riel
2013-03-27 8:40 ` Peter Zijlstra
2013-03-27 8:42 ` Peter Zijlstra
2013-03-27 11:22 ` Michel Lespinasse
2013-03-27 12:02 ` Peter Zijlstra
2013-03-27 20:00 ` Rik van Riel
2013-03-28 20:23 ` [PATCH v2 " Rik van Riel
2013-03-29 2:50 ` Michel Lespinasse
2013-03-29 9:57 ` Peter Zijlstra
2013-03-29 13:21 ` Michel Lespinasse
2013-03-29 12:07 ` Rik van Riel
2013-03-29 13:08 ` Michel Lespinasse
2013-03-29 13:24 ` Rik van Riel
2013-03-29 13:55 ` [PATCH v3 " Rik van Riel
2013-03-29 13:59 ` Michel Lespinasse
2013-03-26 14:25 ` [PATCH " Rik van Riel
2013-03-26 17:33 ` ipc,sem: sysv semaphore scalability Sasha Levin
2013-03-26 17:51 ` Davidlohr Bueso
2013-03-26 18:07 ` Sasha Levin
2013-03-26 18:17 ` Rik van Riel
2013-03-26 20:00 ` [PATCH -mm -next] ipc,sem: untangle RCU locking with find_alloc_undo Rik van Riel
2013-04-05 4:38 ` Mike Galbraith
2013-04-05 13:21 ` Rik van Riel
2013-04-05 16:26 ` Mike Galbraith
2013-04-16 12:37 ` Mike Galbraith
2013-03-26 17:55 ` ipc,sem: sysv semaphore scalability Paul E. McKenney
2013-03-28 15:32 ` [PATCH -mm -next] ipc,sem: untangle RCU locking with find_alloc_undo Rik van Riel
2013-03-28 21:05 ` Davidlohr Bueso
2013-03-29 1:00 ` Michel Lespinasse
2013-03-29 1:14 ` Sasha Levin
2013-03-30 13:35 ` Sasha Levin
2013-03-31 1:30 ` Rik van Riel
2013-03-31 4:09 ` Davidlohr Bueso
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