linux-kernel - Re: [PATCH] Revert "ipc,sem: remove uneeded sem_undo_list lock usage in exit

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Date:   Wed, 18 Dec 2019 20:25:03 +0100
From:   Manfred Spraul <manfred@...orfullife.com>
To:     "Herton R. Krzesinski" <herton@...hat.com>
Cc:     Ioanna Alifieraki <ioanna-maria.alifieraki@...onical.com>,
        akpm@...ux-foundation.org, arnd@...db.de, catalin.marinas@....com,
        malat@...ian.org, joel@...lfernandes.org, gustavo@...eddedor.com,
        linux-kernel@...r.kernel.org, jay.vosburgh@...onical.com,
        ioanna.alifieraki@...il.com
Subject: Re: [PATCH] Revert "ipc,sem: remove uneeded sem_undo_list lock usage
 in exit_sem()"

Hello together,

On 12/17/19 10:17 PM, Herton R. Krzesinski wrote:
> On Mon, Dec 16, 2019 at 08:04:53PM +0100, Manfred Spraul wrote:
>> Hi Ioanna,
>>
>> On 12/11/19 8:13 PM, Ioanna Alifieraki wrote:
>>
>>> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1694779
>>>
>>> Fixes: a97955844807 ("ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()")
>>> Signed-off-by: Ioanna Alifieraki <ioanna-maria.alifieraki@...onical.com>
>> Acked-by: Manfred Spraul <manfred@...orfullife.com>
> Acked-by: Herton R. Krzesinski <herton@...hat.com>

What I forgot:

I think Cc: stable@...r.kernel.org should be added:

The change is obviously correct, it fixes a real issue.

>>> ---
>>>    ipc/sem.c | 6 ++----
>>>    1 file changed, 2 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/ipc/sem.c b/ipc/sem.c
>>> index ec97a7072413..fe12ea8dd2b3 100644
>>> --- a/ipc/sem.c
>>> +++ b/ipc/sem.c
>>> @@ -2368,11 +2368,9 @@ void exit_sem(struct task_struct *tsk)
>>>    		ipc_assert_locked_object(&sma->sem_perm);
>>>    		list_del(&un->list_id);
>>> -		/* we are the last process using this ulp, acquiring ulp->lock
>>> -		 * isn't required. Besides that, we are also protected against
>>> -		 * IPC_RMID as we hold sma->sem_perm lock now
>>> -		 */
>>> +		spin_lock(&ulp->lock);
>>>    		list_del_rcu(&un->list_proc);
>>> +		spin_unlock(&ulp->lock);
>>>    		/* perform adjustments registered in un */
>>>    		for (i = 0; i < sma->sem_nsems; i++) {
>>