From: Manfred Spraul <manfred@colorfullife.com>
To: sedat.dilek@gmail.com, Greg KH <greg@kroah.com>
Cc: 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, 03 Sep 2013 18:33:09 +0200 [thread overview]
Message-ID: <52260F45.6040702@colorfullife.com> (raw)
In-Reply-To: <CA+icZUUdnK3Kc9OFNjcEsZYigbyytsFk90_HaqqUWh9cvq5+0w@mail.gmail.com>
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.
--
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
>>
next prev parent reply other threads:[~2013-09-03 16:33 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 [this message]
2013-09-03 21:56 ` Sedat Dilek
2013-09-03 18:07 ` Davidlohr Bueso
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