From: Omar Sandoval <redacted>

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 <redacted>
---
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);