From: Sedat Dilek <sedat.dilek@gmail.com>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: Greg KH <greg@kroah.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Davidlohr Bueso <dave.bueso@gmail.com>,
Davidlohr Bueso <davidlohr.bueso@hp.com>,
linux-next <linux-next@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
linux-mm <linux-mm@kvack.org>, Andi Kleen <andi@firstfloor.org>,
Rik van Riel <riel@redhat.com>,
Jonathan Gonzalez <jgonzalez@linets.cl>,
Vineet Gupta <Vineet.Gupta1@synopsys.com>
Subject: Re: [PATCH] ipc/msg.c: Fix lost wakeup in msgsnd().
Date: Tue, 3 Sep 2013 23:56:23 +0200 [thread overview]
Message-ID: <CA+icZUUThSZTRTfyLUfutoAHCmkMr1p0MQh7013JY8cto1schA@mail.gmail.com> (raw)
In-Reply-To: <52260F45.6040702@colorfullife.com>
On Tue, Sep 3, 2013 at 6:33 PM, Manfred Spraul <manfred@colorfullife.com> wrote:
> Hi Sedat,
>
>
> On 09/03/2013 06:13 PM, Sedat Dilek wrote:
>>
>> On Tue, Sep 3, 2013 at 4:00 PM, Manfred Spraul <manfred@colorfullife.com>
>> wrote:
>>>
>>> The check if the queue is full and adding current to the wait queue of
>>> pending
>>> msgsnd() operations (ss_add()) must be atomic.
>>>
>>> Otherwise:
>>> - the thread that performs msgsnd() finds a full queue and decides to
>>> sleep.
>>> - the thread that performs msgrcv() calls first reads all messages from
>>> the
>>> queue and then sleep, because the queue is empty.
>>
>> reads -> sleeps
>
> Correct.
>
>>> - the msgrcv() calls do not perform any wakeups, because the msgsnd()
>>> task
>>> has not yet called ss_add().
>>> - then the msgsnd()-thread first calls ss_add() and then sleeps.
>>> Net result: msgsnd() and msgrcv() both sleep forever.
>>>
>> I don't know what and why "net result" - net in sense of networking?
>
> http://en.wiktionary.org/wiki/net#Adjective
> I.e.: Ignore/remove the "Net".
>
>
>>> Observed with msgctl08 from ltp with a preemptible kernel.
>>>
>> ...on ARC arch (that sounds funny somehow).
>>
>>> Fix: Call ipc_lock_object() before performing the check.
>>>
>>> The patch also moves security_msg_queue_msgsnd() under ipc_lock_object:
>>> - msgctl(IPC_SET) explicitely mentions that it tries to expunge any
>>> pending
>>> operations that are not allowed anymore with the new permissions.
>>> If security_msg_queue_msgsnd() is called without locks, then there
>>> might be
>>> races.
>>> - it makes the patch much simpler.
>>>
>>> Reported-by: Vineet Gupta <Vineet.Gupta1@synopsys.com>
>>> Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
>>
>> I guess this is missing a "CC: stable" as Vineet reported against
>> Linux v3.11-rc7 (and should enter v3.11.1)?
>
> Yes. I didn't notice that Linus already released 3.11.
>
Linus pushed your patch upstream... with typos fixed and "CC: stable #3.11".
Thanks to all involved people!
- Sedat -
[1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=bebcb928c820d0ee83aca4b192adc195e43e66a2
> --
> Manfred
>
>> - Sedat -
>>
>>> ---
>>> ipc/msg.c | 12 +++++-------
>>> 1 file changed, 5 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/ipc/msg.c b/ipc/msg.c
>>> index 9f29d9e..b65fdf1 100644
>>> --- a/ipc/msg.c
>>> +++ b/ipc/msg.c
>>> @@ -680,16 +680,18 @@ long do_msgsnd(int msqid, long mtype, void __user
>>> *mtext,
>>> goto out_unlock1;
>>> }
>>>
>>> + ipc_lock_object(&msq->q_perm);
>>> +
>>> for (;;) {
>>> struct msg_sender s;
>>>
>>> err = -EACCES;
>>> if (ipcperms(ns, &msq->q_perm, S_IWUGO))
>>> - goto out_unlock1;
>>> + goto out_unlock0;
>>>
>>> err = security_msg_queue_msgsnd(msq, msg, msgflg);
>>> if (err)
>>> - goto out_unlock1;
>>> + goto out_unlock0;
>>>
>>> if (msgsz + msq->q_cbytes <= msq->q_qbytes &&
>>> 1 + msq->q_qnum <= msq->q_qbytes) {
>>> @@ -699,10 +701,9 @@ long do_msgsnd(int msqid, long mtype, void __user
>>> *mtext,
>>> /* queue full, wait: */
>>> if (msgflg & IPC_NOWAIT) {
>>> err = -EAGAIN;
>>> - goto out_unlock1;
>>> + goto out_unlock0;
>>> }
>>>
>>> - ipc_lock_object(&msq->q_perm);
>>> ss_add(msq, &s);
>>>
>>> if (!ipc_rcu_getref(msq)) {
>>> @@ -730,10 +731,7 @@ long do_msgsnd(int msqid, long mtype, void __user
>>> *mtext,
>>> goto out_unlock0;
>>> }
>>>
>>> - ipc_unlock_object(&msq->q_perm);
>>> }
>>> -
>>> - ipc_lock_object(&msq->q_perm);
>>> msq->q_lspid = task_tgid_vnr(current);
>>> msq->q_stime = get_seconds();
>>>
>>> --
>>> 1.8.3.1
>>>
>
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next prev parent reply other threads:[~2013-09-03 21:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-03 14:00 [PATCH] ipc/msg.c: Fix lost wakeup in msgsnd() Manfred Spraul
2013-09-03 15:08 ` Rik van Riel
2013-09-03 16:13 ` Sedat Dilek
2013-09-03 16:33 ` Manfred Spraul
2013-09-03 21:56 ` Sedat Dilek [this message]
2013-09-03 18:07 ` Davidlohr Bueso
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