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Juergen Gross
9dc8cf0df2
commit 2ac2a7d4d9 upstream.
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()
frees the lock
-> xen_qlock_kick(cpu2)
-> xen_clear_irq_pending()
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>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
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