Remove the unnecessary "!atomic_read(&sh->count)" check, as the previous
"atomic_inc_not_zero(&sh->count)" check assures sh->count to be 0.
The only reason I can think of that we need such check is to consider
the lock race issue.
First of all, I doubt there is another process could modify an in-cache
but zero referenced sh while it's being protected by a hash lock. Hence,
I would say sh->count will be consistent to 0 in that "if !atomic_inc_not_zero"
block.
Secondly, just assume there is a chance that someone outside the lock
modifies sh->count(by atomic_inc?). It could lead to some problem.
To make it clear, here I paste few lines of key code:
if (!atomic_inc_not_zero(&sh->count)) {
spin_lock(&conf->device_lock);
if (!atomic_read(&sh->count)) {
....
}
...
}
At the time we enter the first if block, sh->count is zero. And just assume
someone increases sh->count from somewhere while acquiring the lock,
the following if block will not be executed then, leaving some fileds,
such as conf->active_stripes, not being set properly.
So, we should execute the second if block whenever we entered the first
if block no matter sh->count stays with 0 or not.
Signed-off-by: Yuanhan Liu <yuanhan.liu@xxxxxxxxxxxxxxx>
---
Neil, I'm a bit concerned that I missed something in this patch. Please
kindly correct me if I'm wrong :)
---
drivers/md/raid5.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e7fa818..17ece2a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -570,16 +570,14 @@ static struct stripe_head *__find_stripe(struct r5conf *conf, sector_t sector,
if (sh->sector == sector && sh->generation == generation) {
if (!atomic_inc_not_zero(&sh->count)) {
spin_lock(&conf->device_lock);
- if (!atomic_read(&sh->count)) {
- if (!test_bit(STRIPE_HANDLE, &sh->state))
- atomic_inc(&conf->active_stripes);
- BUG_ON(list_empty(&sh->lru) &&
- !test_bit(STRIPE_EXPANDING, &sh->state));
- list_del_init(&sh->lru);
- if (sh->group) {
- sh->group->stripes_cnt--;
- sh->group = NULL;
- }
+ if (!test_bit(STRIPE_HANDLE, &sh->state))
+ atomic_inc(&conf->active_stripes);
+ BUG_ON(list_empty(&sh->lru) &&
+ !test_bit(STRIPE_EXPANDING, &sh->state));
+ list_del_init(&sh->lru);
+ if (sh->group) {
+ sh->group->stripes_cnt--;
+ sh->group = NULL;
}
atomic_inc(&sh->count);
spin_unlock(&conf->device_lock);
--
1.9.0
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