Re: [PATCH] i386: fix file_read_actor() and pipe_read() for original i386 systems

[Ingo Molnar]

* Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>

Acked-by: Ingo Molnar <mingo@xxxxxxx>

	Ingo
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