Xen devel - Jul 2005 - get_page put_page cmpxchg problem?

Hi Folks,
In -unstable (I haven''t updated in a few days), I''m
investigating a
problem in which revalidate_l1() fails because get_page() fails due to a
count_info of 0.  While that problem is still hanging over me, I did
notice that get_page() in include/asm-x86/mm.h does a 64-bit cmpxchg
while put_page() only does a 32-bit cmpxchg.  Seemed odd to me and
possibly related to my bug.    I''m running on a 32-bit machine without
shadow tables.
 
Can anyone offer an explanation?
 
Thanks for your time,
-steve


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On 21 Jul 2005, at 21:59, King, Steven R wrote:
> Hi Folks,
> In -unstable (I haven''t updated in a few days),
I''m investigating a
> problem in which revalidate_l1() fails because get_page() fails due to 
> a count_info of 0.  While that problem is still hanging over me, I did 
> notice that get_page() in include/asm-x86/mm.h does a 64-bit cmpxchg 
> while put_page() only does a 32-bit cmpxchg.  Seemed odd to me and 
> possibly related to my bug.    I''m running on a 32-bit machine
without
> shadow tables.
>  
> Can anyone offer an explanation?
In put_page() we can be sure the refcnt is non-zero and so the domain 
ptr will not change under our feet. Therefore there''s no need to 
include it in the cmpxchg when we update the reference count.

  -- Keir


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