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From: Andi Kleen <ak@suse.de>
To: Roland Dreier <roland@topspin.com>
Cc: jakub@redhat.com, ak@suse.de, ecd@skynet.be, pavel@suse.cz,
	discuss@x86-64.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fs/compat.c: rwsem instead of BKL around ioctl32_hash_table
Date: Thu, 2 Sep 2004 23:14:48 +0200	[thread overview]
Message-ID: <20040902211448.GE16175@wotan.suse.de> (raw)
In-Reply-To: <524qmi2e1s.fsf@topspin.com>

On Wed, Sep 01, 2004 at 08:40:15AM -0700, Roland Dreier wrote:
> Currently the BKL is used to synchronize access to ioctl32_hash_table
> in fs/compat.c.  It seems that an rwsem would be more appropriate,
> since this would allow multiple lookups to occur in parallel (and also
> serve the general good of minimizing use of the BKL).
> 
> I added lock_kernel()/unlock_kernel() around the call to t->handler
> when a compatibility handler is found in compat_sys_ioctl() to
> preserve the expectation that the BKL will be held during driver ioctl
> operations.  It should be safe to do lock_kernel() while holding
> ioctl32_sem because of the magic BKL sleep semantics.
> 
> I have booted this and run some basic 32-bit userspace on ppc64, and
> also compile tested this for x86_64 and sparc64.

It does not make much sense because the ioctl will take the BKL 
anyways.

If you wanted to fix it properly better make it use RCU - 
but it cannot work for the case of calling a compat handler.

-Andi

  parent reply	other threads:[~2004-09-02 21:18 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-09-01  7:22 f_ops flag to speed up compatible ioctls in linux kernel Michael S. Tsirkin
2004-09-01  7:32 ` viro
2004-09-01  7:44   ` Michael S. Tsirkin
2004-09-01  7:47   ` Lee Revell
2004-09-01  8:19     ` Michael S. Tsirkin
2004-09-01 15:55   ` Roland Dreier
2004-09-01 18:02     ` Chris Wright
2004-09-01 18:12       ` Roland Dreier
2004-09-01 18:31         ` viro
2004-09-01 20:54       ` Roland Dreier
     [not found]         ` <20040901170800.K1924@build.pdx.osdl.net>
     [not found]           ` <20040901190122.L1924@build.pdx.osdl.net>
2004-09-02  3:46             ` Roland Dreier
2004-09-01 18:06   ` Bill Davidsen
2004-09-01  8:30 ` Arjan van de Ven
2004-09-01 15:40 ` [PATCH] fs/compat.c: rwsem instead of BKL around ioctl32_hash_table Roland Dreier
2004-09-01 23:27   ` Andrew Morton
2004-09-02 21:14   ` Andi Kleen [this message]
2004-09-02 22:26     ` Roland Dreier
2004-09-03 14:37       ` [discuss] " Andi Kleen
2004-09-03 14:55         ` Roland Dreier
2004-09-03 15:02           ` Andi Kleen
2004-09-03  8:00 ` [discuss] f_ops flag to speed up compatible ioctls in linux kernel Andi Kleen
2004-09-07 10:40   ` Michael S. Tsirkin
2004-09-07 12:14     ` Andi Kleen
2004-09-07 13:45       ` Michael S. Tsirkin
2004-09-07 14:15         ` Andi Kleen
2004-09-07 14:25           ` Michael S. Tsirkin
2004-09-07 14:29             ` Andi Kleen
2004-09-07 14:37               ` Michael S. Tsirkin
2004-09-07 14:44                 ` Andi Kleen
2004-09-07 14:45                   ` Michael S. Tsirkin
2004-09-07 15:10                     ` Andi Kleen
2004-09-07 18:16                       ` Michael S. Tsirkin
2004-09-08  6:55                         ` Andi Kleen
2004-09-08 14:28                           ` [patch] " Michael S. Tsirkin
2004-09-08 14:38                             ` Andi Kleen
2004-09-08 14:54                               ` Michael S. Tsirkin
2004-09-08 14:58                                 ` Andi Kleen
2004-09-12 20:05                                   ` Michael S. Tsirkin
2004-09-15 13:19                               ` [patch] Re: [discuss] " Michael S. Tsirkin
2004-09-07 21:36                       ` Is FIOQSIZE compatible? ( was Re: f_ops flag to speed up compatible ioctls in linux kernel) Michael S. Tsirkin
2004-09-08  6:54                         ` Andi Kleen
2004-09-07 15:03               ` [discuss] f_ops flag to speed up compatible ioctls in linux kernel Herbert Poetzl
2004-09-07 18:07                 ` Michael S. Tsirkin
2004-09-09 13:54                   ` Herbert Poetzl
2004-12-12 21:51       ` how to detect a 32 bit process on 64 bit kernel Michael S. Tsirkin
2004-12-12 22:01         ` Jan Engelhardt
2004-12-12 22:23         ` Christoph Hellwig
2004-12-13 19:50           ` Michael S. Tsirkin
2004-12-13 21:01             ` Jan Engelhardt
2004-12-13 21:32             ` Brian Gerst
2004-12-13 21:37               ` Michael S. Tsirkin
2004-12-12 22:37         ` Willy Tarreau
2004-12-12 23:30           ` Bongani Hlope
2004-12-14  7:28         ` Andi Kleen
2004-09-20 14:49   ` [patch] speed up ioctls in linux kernel Michael S. Tsirkin

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