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authorOmar Sandoval <osandov@fb.com>2017-12-05 22:57:43 -0800
committerJens Axboe <axboe@kernel.dk>2017-12-06 12:33:07 -0700
commitfcf38cdf332a81b20a59e3ebaea81f6b316bbe0c (patch)
tree0e6b81c6bb908381eb851ef1a334a56943e9be6d
parentae64f9bd1d3621b5e60d7363bc20afb46aede215 (diff)
downloadlinux-0-day-fcf38cdf332a81b20a59e3ebaea81f6b316bbe0c.tar.gz
kyber: fix another domain token wait queue hang
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 of 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 <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--block/kyber-iosched.c37
1 files changed, 24 insertions, 13 deletions
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index b4df317..f95c607 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]);
+ khd->domain_ws[sched_domain] = ws;
add_wait_queue(&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;
}