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xen: make xen_qlock_wait() nestable

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xen_qlock_wait() isn't safe for nested calls due to interrupts. A call
of xen_qlock_kick() might be ignored in case a deeper nesting level
was active right before the call of xen_poll_irq():

CPU 1:                                   CPU 2:
spin_lock(lock1)
                                         spin_lock(lock1)
                                         -> xen_qlock_wait()
                                            -> xen_clear_irq_pending()
                                            Interrupt happens
spin_unlock(lock1)
-> xen_qlock_kick(CPU 2)
spin_lock_irqsave(lock2)
                                         spin_lock_irqsave(lock2)
                                         -> xen_qlock_wait()
                                            -> xen_clear_irq_pending()
                                               clears kick for lock1
                                            -> xen_poll_irq()
spin_unlock_irq_restore(lock2)
-> xen_qlock_kick(CPU 2)
                                            wakes up
                                         spin_unlock_irq_restore(lock2)
                                         IRET
                                           resumes in xen_qlock_wait()
                                           -> xen_poll_irq()
                                           never wakes up

The solution is to disable interrupts in xen_qlock_wait() and not to
poll for the irq in case xen_qlock_wait() is called in nmi context.

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>
This commit is contained in:
Juergen Gross 2018-10-01 07:57:42 +02:00
parent 2ac2a7d4d9
commit a856531951
1 changed files with 10 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
arch/x86/xen/spinlock.c
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@ -39,29 +39,25 @@ static void xen_qlock_kick(int cpu)
*/
static void xen_qlock_wait(u8 *byte, u8 val)
{
unsigned long flags;
int irq = __this_cpu_read(lock_kicker_irq);
/* If kicker interrupts not initialized yet, just spin */
if (irq == -1)
if (irq == -1 || in_nmi())
return;
/* If irq pending already clear it and return. */
/* Guard against reentry. */
local_irq_save(flags);
/* If irq pending already clear it. */
if (xen_test_irq_pending(irq)) {
xen_clear_irq_pending(irq);
return;
} else if (READ_ONCE(*byte) == val) {
/* Block until irq becomes pending (or a spurious wakeup) */
xen_poll_irq(irq);
}
if (READ_ONCE(*byte) != val)
return;
/*
* If an interrupt happens here, it will leave the wakeup irq
* pending, which will cause xen_poll_irq() to return
* immediately.
*/
/* Block until irq becomes pending (or perhaps a spurious wakeup) */
xen_poll_irq(irq);
local_irq_restore(flags);
}
static irqreturn_t dummy_handler(int irq, void *dev_id)