| Message ID | 20201104081549.3712-3-jgross@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xen/locking: fix and enhance lock debugging | expand |
Hi Juergen, On 04/11/2020 08:15, Juergen Gross wrote: > Spinlocks and rwlocks behave differently in the try variants regarding > preemption: rwlocks are switching preemption off before testing the > lock, while spinlocks do so only after the first check. > > Modify _spin_trylock() to disable preemption before testing the lock > to be held in order to be preemption-ready. > > Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Julien Grall <jgrall@amazon.com> Cheers,
diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c index b4aaf6bce6..f4eb50f030 100644 --- a/xen/common/spinlock.c +++ b/xen/common/spinlock.c @@ -240,13 +240,16 @@ int _spin_trylock(spinlock_t *lock) { spinlock_tickets_t old, new; + preempt_disable(); check_lock(&lock->debug, true); old = observe_lock(&lock->tickets); if ( old.head != old.tail ) + { + preempt_enable(); return 0; + } new = old; new.tail++; - preempt_disable(); if ( cmpxchg(&lock->tickets.head_tail, old.head_tail, new.head_tail) != old.head_tail ) {
Spinlocks and rwlocks behave differently in the try variants regarding preemption: rwlocks are switching preemption off before testing the lock, while spinlocks do so only after the first check. Modify _spin_trylock() to disable preemption before testing the lock to be held in order to be preemption-ready. Signed-off-by: Juergen Gross <jgross@suse.com> --- V3: - new patch --- xen/common/spinlock.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)