linux-kernel - Re: [patch 1/1] Switch ioctl functions of drivers/scsi/sg.c to unlocked

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Date:	Thu, 10 Jan 2008 21:40:20 +0100
From:	Andre Noll <maan@...temlinux.org>
To:	Boaz Harrosh <bharrosh@...asas.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Richard Knutsson <ricknu-0@...dent.ltu.se>
Subject: Re: [patch 1/1] Switch ioctl functions of drivers/scsi/sg.c to unlocked_ioctl

On 22:13, Boaz Harrosh wrote:

> All the scsi calls do not need any locks. The scsi LLDS never
> see these threads since commands are queued through the block
> layer.

That's what everybody believes, but nobody seems to know for sure.
Therefore I did what Andi suggested: Make a zero-semantics change
that moves the lock_kernel() to sg_ioctl() to make people aware of
the fact that this function runs under the BKL. At least the latter
has already succeeded.

> What's left is what you see, here in sg.c. you must have the best 
> knowledge about the possible races between ioctl and open/release
> and probe/remove. And all these put_user() copy_user() etc...
> Why don't you have a hard look and fix them properly.

Because that requires much more knowledge. Al is looking into this
which indicates that it is non-trivial issue. I am clearly not the
right person to decide this question.

> please don't *lock_kernel();* for scsi's sake.

The BKL was there all the time. My patch just made it more visable
to the scsi people by moving it into sg.c.

Andre
-- 
The only person who always got his work done by Friday was Robinson Crusoe

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