* Re: [Xen-devel] [PATCH 1/2] xen: fix race in xen_qlock_wait()
@ 2018-10-01 8:58 Juergen Gross
0 siblings, 0 replies; 2+ messages in thread
From: Juergen Gross @ 2018-10-01 8:58 UTC (permalink / raw)
To: Jan Beulich
Cc: Borislav Petkov, Peter Zijlstra, the arch/x86 maintainers,
Thomas Gleixner, xen-devel, Boris Ostrovsky, longman, mingo,
lkml, stable, H. Peter Anvin
On 01/10/2018 10:54, Jan Beulich wrote:
>>>> On 01.10.18 at 09:16, <jgross@suse.com> wrote:
>> In the following situation a vcpu waiting for a lock might not be
>> woken up from xen_poll_irq():
>>
>> CPU 1: CPU 2: CPU 3:
>> takes a spinlock
>> tries to get lock
>> -> xen_qlock_wait()
>> -> xen_clear_irq_pending()
>
> Doesn't the last line above ...
>
>> frees the lock
>> -> xen_qlock_kick(cpu2)
>
> ... need to be below here?
You are right, of course!
Thanks for noticing.
Juergen
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [Xen-devel] [PATCH 1/2] xen: fix race in xen_qlock_wait()
2018-10-01 7:16 ` [PATCH 1/2] xen: fix race in xen_qlock_wait() Juergen Gross
@ 2018-10-01 8:54 ` Jan Beulich
0 siblings, 0 replies; 2+ messages in thread
From: Jan Beulich @ 2018-10-01 8:54 UTC (permalink / raw)
To: Juergen Gross
Cc: Borislav Petkov, Peter Zijlstra, the arch/x86 maintainers, tglx,
xen-devel, Boris Ostrovsky, longman, mingo, linux-kernel, stable,
hpa
>>> On 01.10.18 at 09:16, <jgross@suse.com> wrote:
> In the following situation a vcpu waiting for a lock might not be
> woken up from xen_poll_irq():
>
> CPU 1: CPU 2: CPU 3:
> takes a spinlock
> tries to get lock
> -> xen_qlock_wait()
> -> xen_clear_irq_pending()
Doesn't the last line above ...
> frees the lock
> -> xen_qlock_kick(cpu2)
... need to be below here?
> takes lock again
> tries to get lock
> -> *lock = _Q_SLOW_VAL
> -> *lock == _Q_SLOW_VAL ?
> -> xen_poll_irq()
> frees the lock
> -> xen_qlock_kick(cpu3)
>
> And cpu 2 will sleep forever.
>
> This can be avoided easily by modifying xen_qlock_wait() to call
> xen_poll_irq() only if the related irq was not pending and to call
> xen_clear_irq_pending() only if it was pending.
>
> Cc: stable@vger.kernel.org
> Cc: Waiman.Long@hp.com
> Cc: peterz@infradead.org
> Signed-off-by: Juergen Gross <jgross@suse.com>
Patch itself
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Jan
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2018-10-01 8:58 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-10-01 8:58 [Xen-devel] [PATCH 1/2] xen: fix race in xen_qlock_wait() Juergen Gross
-- strict thread matches above, loose matches on Subject: below --
2018-10-01 7:16 [PATCH 0/2] xen: fix two issues in Xen pv qspinlock handling Juergen Gross
2018-10-01 7:16 ` [PATCH 1/2] xen: fix race in xen_qlock_wait() Juergen Gross
2018-10-01 8:54 ` [Xen-devel] " Jan Beulich
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