linux-kernel - Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock

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Date:	Tue, 13 Jul 2010 16:19:02 +0200
From:	Peter Palfrader <peter@...frader.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	stable@...nel.org, stable-review@...nel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Glauber Costa <glommer@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [patch 134/149] x86, paravirt: Add a global synchronization
	point for pvclock

On Tue, 13 Jul 2010, Avi Kivity wrote:

>> BUG: unable to handle kernel paging request at ffffffff81712e80
>> IP: [<ffffffff81054f73>] pvclock_clocksource_read+0x83/0xc0
>> PGD 1003067 PUD 1007063 PMD 7e8b1063 PTE 8000000001712161
> Read-only pte
>> Oops: 0003 [#2] SMP
> Write fault.
>> Code: 78 4f 44 89 e1 48 d3 e0 44 89 f2 48 f7 e2 48 0f ac d0 20 4a 8d 0c 38 44 39 03 75 a4 48 8b 15 15 df 6b 00 48 39 ca 77 17 48 89 d0<f0>  48 0f b1 0d 04 df 6b 00 48 39 c1 48 89 c2 75 e7 48 89 ca 48
>> RIP  [<ffffffff81054f73>] pvclock_clocksource_read+0x83/0xc0
> --> lock cmpxchg %rcx,0x6bdf04(%rip)


>> static atomic64_t last_value = ATOMIC64_INIT(0);
>>
>> cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
>>         last = atomic64_cmpxchg(&last_value, last, ret);


> So it looks like last_value was placed in a read only section.  Please  
> post your System.map somewhere.

weasel@...repid:~$ publish System.map
http://asteria.noreply.org/~weasel/volatile/2010-07-13-mbm2xEdd8Q4/System.map
weasel@...repid:~$ grep -i last_value System.map
ffffffff81712e80 r last_value
ffffffff81b05240 b last_value.26163

Cheers,
Peter
-- 
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