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xen: only enable interrupts while actually blocking for spinlock 

Where possible we enable interrupts while waiting for a spinlock to
become free, in order to reduce big latency spikes in interrupt handling.

However, at present if we manage to pick up the spinlock just before
blocking, we'll end up holding the lock with interrupts enabled for a
while.  This will cause a deadlock if we recieve an interrupt in that
window, and the interrupt handler tries to take the lock too.

Solve this by shrinking the interrupt-enabled region to just around the
blocking call.

[ Impact: avoid race/deadlock when using Xen PV spinlocks ]

Reported-by: "Yang, Xiaowei" <xiaowei.yang@intel.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
This commit is contained in:
Jeremy Fitzhardinge 2009-09-09 12:33:51 -07:00
parent 577eebeae3
commit 4d576b57b5
1 changed files with 11 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
arch/x86/xen/spinlock.c
View File

@ -187,7 +187,6 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl
struct xen_spinlock *prev;
int irq = __get_cpu_var(lock_kicker_irq);
int ret;
unsigned long flags;
u64 start;
/* If kicker interrupts not initialized yet, just spin */
@ -199,16 +198,12 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl
/* announce we're spinning */
prev = spinning_lock(xl);
flags = __raw_local_save_flags();
if (irq_enable) {
ADD_STATS(taken_slow_irqenable, 1);
raw_local_irq_enable();
}
ADD_STATS(taken_slow, 1);
ADD_STATS(taken_slow_nested, prev != NULL);
do {
unsigned long flags;
/* clear pending */
xen_clear_irq_pending(irq);
@ -228,6 +223,12 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl
goto out;
}
flags = __raw_local_save_flags();
if (irq_enable) {
ADD_STATS(taken_slow_irqenable, 1);
raw_local_irq_enable();
}
/*
* Block until irq becomes pending. If we're
* interrupted at this point (after the trylock but
@ -238,13 +239,15 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl
* pending.
*/
xen_poll_irq(irq);
raw_local_irq_restore(flags);
ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
} while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
out:
raw_local_irq_restore(flags);
unspinning_lock(xl, prev);
spin_time_accum_blocked(start);