linux-kernel - Re: [PATCH -mm] ipc,sem: fix locking in semctl

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Date:	Tue, 23 Apr 2013 20:06:04 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Davidlohr Bueso <davidlohr.bueso@...com>
Cc:	Rik van Riel <riel@...hat.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Emmanuel Benisty <benisty.e@...il.com>
Subject: Re: [PATCH -mm] ipc,sem: fix locking in semctl_main

On Tue, Apr 23, 2013 at 7:36 PM, Davidlohr Bueso <davidlohr.bueso@...com> wrote:
> On Tue, 2013-04-23 at 12:29 -0400, Rik van Riel wrote:
>> Andrew, here is the patch I promised :)
>>
>> Everywhere else in the code, we check sma->sem_perm.deleted under
>> the semaphore array lock, so we should do teh same here.
>> The easy fix is to simply not drop and re-take the lock, but keep
>> it locked.
>>
>
> CCing Linus, Sedat and Emmanuel.
>
> This looks very much like a patch I asked Sedat to test during the
> weekend, which according to him didn't solve his issue. The patch is
> correct in any case.
>

Your patch looked a bit different (checked for ipc-lock already taken,
both patches - original and refreshed againt -next attached).

- Sedat -

>> This patch can be folded into ipcsem-fine-grained-locking-for-semtimedop.patch
>>
>> Signed-off-by: Rik van Riel <riel@...hat.com>
>
> Acked-by: Davidlohr Bueso <davidlohr.bueso@...com>
>
>> ---
>>  ipc/sem.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/ipc/sem.c b/ipc/sem.c
>> index 5711616..efdaee6 100644
>> --- a/ipc/sem.c
>> +++ b/ipc/sem.c
>> @@ -1243,10 +1243,9 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
>>                               err = -EIDRM;
>>                               goto out_free;
>>                       }
>> -                     sem_unlock(sma, -1);
>> -             }
>> +             } else
>> +                     sem_lock(sma, NULL, -1);
>>
>> -             sem_lock(sma, NULL, -1);
>>               for (i = 0; i < sma->sem_nsems; i++)
>>                       sem_io[i] = sma->sem_base[i].semval;
>>               sem_unlock(sma, -1);
>
>

Download attachment "ipc-fix.patch" of type "application/octet-stream" (721 bytes)

Download attachment "ipc-fix-v2.patch" of type "application/octet-stream" (836 bytes)