Re: [PATCH] bcache: Make gc wakeup sane, remove set_task_state()

[Coly Li <colyli@suse.de>]

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On 2017/2/20 下午10:06, Greg KH wrote:
> On Mon, Feb 20, 2017 at 04:12:58AM -0900, Kent Overstreet wrote:
>> On Mon, Feb 20, 2017 at 01:31:37PM +0100, Greg KH wrote:
>>> On Mon, Jan 23, 2017 at 03:54:07PM +0100, Greg KH wrote:
>>>> Kent, any hints?
>>>
>>> Without a response from the maintainer, I can't apply this...
>>>
>>> greg k-h
>>
>> Sorry I missed this - yes, this patch should be safe to apply and it does fix
>> that crash. The relevant code hasn't been changed in ages, 4.4 is definitely
>> fine.
> 
> Ok, I've queued this up for 4.9, but for 4.4 it does not apply.  Coly,
> can you provide a working backport for 4.4-stable?

Greg,

It is because the 'commit 29e6c57cc78e ("bcache: bch_gc_thread() is not
freezable")' remove a "try_to_freeze()" in bch_gc_thread(), which
happens in v4.7.

I just rebase Kent's fix to v4.4 kernel, solve the conflict. Could you
please check and try the attached patch ?

Thanks.

Coly

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Subject: [PATCH] bcache: Make gc wakeup sane, remove set_task_state()

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
---
 drivers/md/bcache/bcache.h  |  4 ++--
 drivers/md/bcache/btree.c   | 40 ++++++++++++++++++++--------------------
 drivers/md/bcache/btree.h   |  3 +--
 drivers/md/bcache/request.c |  4 +---
 drivers/md/bcache/super.c   |  2 ++
 5 files changed, 26 insertions(+), 27 deletions(-)

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 6b420a5..c3ea03c 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -425,7 +425,7 @@ struct cache {
 	 * until a gc finishes - otherwise we could pointlessly burn a ton of
 	 * cpu
 	 */
-	unsigned		invalidate_needs_gc:1;
+	unsigned		invalidate_needs_gc;
 
 	bool			discard; /* Get rid of? */
 
@@ -593,8 +593,8 @@ struct cache_set {
 
 	/* Counts how many sectors bio_insert has added to the cache */
 	atomic_t		sectors_to_gc;
+	wait_queue_head_t	gc_wait;
 
-	wait_queue_head_t	moving_gc_wait;
 	struct keybuf		moving_gc_keys;
 	/* Number of moving GC bios in flight */
 	struct semaphore	moving_in_flight;
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 83392f8..b5eccb5 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -1761,33 +1761,34 @@ static void bch_btree_gc(struct cache_set *c)
 	bch_moving_gc(c);
 }
 
-static int bch_gc_thread(void *arg)
+static bool gc_should_run(struct cache_set *c)
 {
-	struct cache_set *c = arg;
 	struct cache *ca;
 	unsigned i;
 
-	while (1) {
-again:
-		bch_btree_gc(c);
+	for_each_cache(ca, c, i)
+		if (ca->invalidate_needs_gc)
+			return true;
 
-		set_current_state(TASK_INTERRUPTIBLE);
-		if (kthread_should_stop())
-			break;
+	if (atomic_read(&c->sectors_to_gc) < 0)
+		return true;
 
-		mutex_lock(&c->bucket_lock);
+	return false;
+}
 
-		for_each_cache(ca, c, i)
-			if (ca->invalidate_needs_gc) {
-				mutex_unlock(&c->bucket_lock);
-				set_current_state(TASK_RUNNING);
-				goto again;
-			}
+static int bch_gc_thread(void *arg)
+{
+	struct cache_set *c = arg;
 
-		mutex_unlock(&c->bucket_lock);
+	while (1) {
+		wait_event_interruptible(c->gc_wait,
+			   kthread_should_stop() || gc_should_run(c));
 
-		try_to_freeze();
-		schedule();
+		if (kthread_should_stop())
+			break;
+
+		set_gc_sectors(c);
+		bch_btree_gc(c);
 	}
 
 	return 0;
@@ -1795,11 +1796,10 @@ again:
 
 int bch_gc_thread_start(struct cache_set *c)
 {
-	c->gc_thread = kthread_create(bch_gc_thread, c, "bcache_gc");
+	c->gc_thread = kthread_run(bch_gc_thread, c, "bcache_gc");
 	if (IS_ERR(c->gc_thread))
 		return PTR_ERR(c->gc_thread);
 
-	set_task_state(c->gc_thread, TASK_INTERRUPTIBLE);
 	return 0;
 }
 
diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h
index 5c391fa..9b80417 100644
--- a/drivers/md/bcache/btree.h
+++ b/drivers/md/bcache/btree.h
@@ -260,8 +260,7 @@ void bch_initial_mark_key(struct cache_set *, int, struct bkey *);
 
 static inline void wake_up_gc(struct cache_set *c)
 {
-	if (c->gc_thread)
-		wake_up_process(c->gc_thread);
+	wake_up(&c->gc_wait);
 }
 
 #define MAP_DONE	0
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 25fa844..2410df1 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -196,10 +196,8 @@ static void bch_data_insert_start(struct closure *cl)
 	struct data_insert_op *op = container_of(cl, struct data_insert_op, cl);
 	struct bio *bio = op->bio, *n;
 
-	if (atomic_sub_return(bio_sectors(bio), &op->c->sectors_to_gc) < 0) {
-		set_gc_sectors(op->c);
+	if (atomic_sub_return(bio_sectors(bio), &op->c->sectors_to_gc) < 0)
 		wake_up_gc(op->c);
-	}
 
 	if (op->bypass)
 		return bch_data_invalidate(cl);
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 679a093..81fef23 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1474,6 +1474,7 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
 	mutex_init(&c->bucket_lock);
 	init_waitqueue_head(&c->btree_cache_wait);
 	init_waitqueue_head(&c->bucket_wait);
+	init_waitqueue_head(&c->gc_wait);
 	sema_init(&c->uuid_write_mutex, 1);
 
 	spin_lock_init(&c->btree_gc_time.lock);
@@ -1532,6 +1533,7 @@ static void run_cache_set(struct cache_set *c)
 
 	for_each_cache(ca, c, i)
 		c->nbuckets += ca->sb.nbuckets;
+	set_gc_sectors(c);
 
 	if (CACHE_SYNC(&c->sb)) {
 		LIST_HEAD(journal);
-- 
2.10.2