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authorJuergen Gross <jgross@suse.com>2018-10-01 07:57:42 +0200
committerJuergen Gross <jgross@suse.com>2018-10-24 10:18:04 +0200
commita856531951dc8094359dfdac21d59cee5969c18e (patch)
tree3e87ca7c1afe1453d3aaac82b1ef4eae3114bf88
parent2ac2a7d4d9ff4e01e36f9c3d116582f6f655ab47 (diff)
xen: make xen_qlock_wait() nestable
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>
-rw-r--r--arch/x86/xen/spinlock.c24
1 files changed, 10 insertions, 14 deletions
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 290a69ec7d4d..441c88262169 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -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)