linux-kernel - Re: ipc,sem: sysv semaphore scalability

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Message-ID: <51583E01.5030106@surriel.com>
Date:	Sun, 31 Mar 2013 09:45:37 -0400
From:	Rik van Riel <riel@...riel.com>
To:	Davidlohr Bueso <davidlohr.bueso@...com>
CC:	Emmanuel Benisty <benisty.e@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	hhuang@...hat.com, "Low, Jason" <jason.low2@...com>,
	Michel Lespinasse <walken@...gle.com>,
	Larry Woodman <lwoodman@...hat.com>,
	"Vinod, Chegu" <chegu_vinod@...com>,
	Peter Hurley <peter@...leysoftware.com>
Subject: Re: ipc,sem: sysv semaphore scalability

On 03/31/2013 01:01 AM, Davidlohr Bueso wrote:

> diff --git a/ipc/sem.c b/ipc/sem.c
> index f257afe..74cedfe 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -1867,8 +1867,7 @@ void exit_sem(struct task_struct *tsk)
>   		struct sem_array *sma;
>   		struct sem_undo *un;
>   		struct list_head tasks;
> -		int semid;
> -		int i;
> +		int semid, i;
>
>   		rcu_read_lock();
>   		un = list_entry_rcu(ulp->list_proc.next,
> @@ -1884,12 +1883,13 @@ void exit_sem(struct task_struct *tsk)
>   		}
>
>   		sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, un->semid);

Should we use "semid" here, like Linus suggested, instead of "un->semid"?

> -		sem_lock(sma, NULL, -1);
> -
>   		/* exit_sem raced with IPC_RMID, nothing to do */
> -		if (IS_ERR(sma))
> +		if (IS_ERR(sma)) {
> +			rcu_read_unlock();
>   			continue;
> +		}
>
> +		sem_lock(sma, NULL, -1);
>   		un = __lookup_undo(ulp, semid);
>   		if (un == NULL) {
>   			/* exit_sem raced with IPC_RMID+semget() that created
>

-- 
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