linux-kernel - Re: [PATCH] ipc/sem.c: prevent ENOMEM in semop() w/ SEM

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Date:	Fri, 03 Aug 2012 19:39:02 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Seiichi Ikarashi <s.ikarashi@...fujitsu.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipc/sem.c: prevent ENOMEM in semop() w/ SEM_UNDO flag

Hi Seiichi,

On 08/03/2012 02:49 PM, Seiichi Ikarashi wrote:
> semop() with SEM_UNDO sem_flg can result in ENOMEM even after
> succeeding semget() with large nsems.
How large is nsems, what is the use case?
Which kind of operations are performed?
Only simple semop(,,1) calls?

<linux/sem.h> still documents ~8000 as the upper limit, I'm not sure if
there are other codepaths that might fail as well.
If all are fixed, then the documentation should be updated as well.

>  This is because
> semop() uses kzalloc() via find_alloc_undo() though
> semget() uses vmalloc() via ipc_rcu_alloc().
> This patch makes semop() be able to use vmalloc() via ipc_alloc().
>
> Signed-off-by: Seiichi Ikarashi <s.ikarashi@...fujitsu.com>

--
Manfred
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