There's no need to subtract _QR_BIAS from the lock value for storing
in the local cnts variable in the read lock slow path: the users of
the value in cnts only care about the writer-related bits and use a
mask to get the value.
Note that further setting of cnts in rspin_until_writer_unlock already
do not subtract _QR_BIAS.
Signed-off-by: Roger Pau Monné <roger....@citrix.com>
---
xen/common/rwlock.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/xen/common/rwlock.c b/xen/common/rwlock.c
index dadab372b5..aa15529bbe 100644
--- a/xen/common/rwlock.c
+++ b/xen/common/rwlock.c
@@ -47,7 +47,7 @@ void queue_read_lock_slowpath(rwlock_t *lock)
while ( atomic_read(&lock->cnts) & _QW_WMASK )
cpu_relax();
- cnts = atomic_add_return(_QR_BIAS, &lock->cnts) - _QR_BIAS;
+ cnts = atomic_add_return(_QR_BIAS, &lock->cnts);
rspin_until_writer_unlock(lock, cnts);
/*
--
2.34.1
