From: Omar Sandoval <osan...@fb.com>
Commit 8cf466602028 ("kyber: fix hang on domain token wait queue") fixed
a hang caused by leaving wait entries on the domain token wait queue
after the __sbitmap_queue_get() retry succeeded, making that wait entry
a "dud" which won't in turn wake more entries up. However, we can also
get a dud entry if kyber_get_domain_token() fails once but is then
called again and succeeds. This can happen if the hardware queue is
rerun for some other reason, or, more likely, kyber_dispatch_request()
tries the same domain twice.
The fix is to remove our entry from the wait queue whenever we
successfully get a token. The only complication is that we might be on
one of many wait queues in the struct sbitmap_queue, but that's easily
fixed by remembering which wait queue we were put on.
While we're here, only initialize the wait queue entry once instead on
every wait, and use spin_lock_irq() instead of spin_lock_irqsave(),
since this is always called from process context with irqs enabled.
Signed-off-by: Omar Sandoval <osan...@fb.com>
---
I have another, rarer hang I'm still working out, but I can get this one
out of the way.
block/kyber-iosched.c | 39 +++++++++++++++++++++++++--------------
1 file changed, 25 insertions(+), 14 deletions(-)
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index b4df317c2916..00cf624ce3ed 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -100,9 +100,13 @@ struct kyber_hctx_data {
unsigned int cur_domain;
unsigned int batching;
wait_queue_entry_t domain_wait[KYBER_NUM_DOMAINS];
+ struct sbq_wait_state *domain_ws[KYBER_NUM_DOMAINS];
atomic_t wait_index[KYBER_NUM_DOMAINS];
};
+static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int
flags,
+ void *key);
+
static int rq_sched_domain(const struct request *rq)
{
unsigned int op = rq->cmd_flags;
@@ -385,6 +389,9 @@ static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx,
unsigned int hctx_idx)
for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
INIT_LIST_HEAD(&khd->rqs[i]);
+ init_waitqueue_func_entry(&khd->domain_wait[i],
+ kyber_domain_wake);
+ khd->domain_wait[i].private = hctx;
INIT_LIST_HEAD(&khd->domain_wait[i].entry);
atomic_set(&khd->wait_index[i], 0);
}
@@ -524,35 +531,39 @@ static int kyber_get_domain_token(struct kyber_queue_data
*kqd,
int nr;
nr = __sbitmap_queue_get(domain_tokens);
- if (nr >= 0)
- return nr;
/*
* If we failed to get a domain token, make sure the hardware queue is
* run when one becomes available. Note that this is serialized on
* khd->lock, but we still need to be careful about the waker.
*/
- if (list_empty_careful(&wait->entry)) {
- init_waitqueue_func_entry(wait, kyber_domain_wake);
- wait->private = hctx;
+ if (nr < 0 && list_empty_careful(&wait->entry)) {
ws = sbq_wait_ptr(domain_tokens,
&khd->wait_index[sched_domain]);
- add_wait_queue(&ws->wait, wait);
+ khd->domain_ws[sched_domain] = ws;
+ add_wait_queue_exclusive(&ws->wait, wait);
/*
* Try again in case a token was freed before we got on the wait
- * queue. The waker may have already removed the entry from the
- * wait queue, but list_del_init() is okay with that.
+ * queue.
*/
nr = __sbitmap_queue_get(domain_tokens);
- if (nr >= 0) {
- unsigned long flags;
+ }
- spin_lock_irqsave(&ws->wait.lock, flags);
- list_del_init(&wait->entry);
- spin_unlock_irqrestore(&ws->wait.lock, flags);
- }
+ /*
+ * If we got a token while we were on the wait queue, remove ourselves
+ * from the wait queue to ensure that all wake ups make forward
+ * progress. It's possible that the waker already deleted the entry
+ * between the !list_empty_careful() check and us grabbing the lock, but
+ * list_del_init() is okay with that.
+ */
+ if (nr >= 0 && !list_empty_careful(&wait->entry)) {
+ ws = khd->domain_ws[sched_domain];
+ spin_lock_irq(&ws->wait.lock);
+ list_del_init(&wait->entry);
+ spin_unlock_irq(&ws->wait.lock);
}
+
return nr;
}
--
2.15.1
