linux-kernel - Re: [PATCH] i386: fix file_read_actor() and pipe

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Message-ID: <20070402123449.GB7747@elte.hu>
Date:	Mon, 2 Apr 2007 14:34:49 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Stable Kernel Team <stable@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Adrian Bunk <bunk@...sta.de>,
	Manfred Spraul <manfred@...orfullife.com>
Subject: Re: [PATCH] i386: fix file_read_actor() and pipe_read()  for original i386 systems


* Thomas Gleixner <tglx@...utronix.de> wrote:

> The __copy_to_user_inatomic() calls in file_read_actor() and 
> pipe_read() are broken on original i386 machines, where WP-works-ok == 
> false, as __copy_to_user_inatomic() on such systems calls functions 
> which might sleep and/or contain cond_resched() calls inside of a 
> kmap_atomic() region.
> 
> The original check for WP-works-ok was in access_ok(), but got moved 
> during the 2.5 series to fix a race vs. swap.
> 
> Return the number of bytes to copy in the case where we are in an 
> atomic region, so the non atomic code pathes in file_read_actor() and 
> pipe_read() are taken.

neat trick! (v2.6.21 must-have me thinks.)

> This could be optimized to avoid the kmap_atomicby moving the check 
                                                  ^---- add space
> for WP-works-ok into fault_in_pages_writeable(), but this is more 
> intrusive and can be done later.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Acked-by: Ingo Molnar <mingo@...e.hu>

	Ingo
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