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

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Date:	Tue, 23 Apr 2013 10:36:50 -0700
From:	Davidlohr Bueso <davidlohr.bueso@...com>
To:	Rik van Riel <riel@...hat.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	sedat.dilek@...il.com, Emmanuel Benisty <benisty.e@...il.com>
Subject: Re: [PATCH -mm] ipc,sem: fix locking in semctl_main

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.

> 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);


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