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