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Commit c2437d07 authored by Andrea Righi's avatar Andrea Righi Committed by Greg Kroah-Hartman
Browse files

bcache: fix deadlock in bcache_allocator 

[ Upstream commit 84c529aea182939e68f618ed9813740c9165c7eb ]

bcache_allocator can call the following:

 bch_allocator_thread()
  -> bch_prio_write()
     -> bch_bucket_alloc()
        -> wait on &ca->set->bucket_wait

But the wake up event on bucket_wait is supposed to come from
bch_allocator_thread() itself => deadlock:

[ 1158.490744] INFO: task bcache_allocato:15861 blocked for more than 10 seconds.
[ 1158.495929]       Not tainted 5.3.0-050300rc3-generic #201908042232
[ 1158.500653] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1158.504413] bcache_allocato D    0 15861      2 0x80004000
[ 1158.504419] Call Trace:
[ 1158.504429]  __schedule+0x2a8/0x670
[ 1158.504432]  schedule+0x2d/0x90
[ 1158.504448]  bch_bucket_alloc+0xe5/0x370 [bcache]
[ 1158.504453]  ? wait_woken+0x80/0x80
[ 1158.504466]  bch_prio_write+0x1dc/0x390 [bcache]
[ 1158.504476]  bch_allocator_thread+0x233/0x490 [bcache]
[ 1158.504491]  kthread+0x121/0x140
[ 1158.504503]  ? invalidate_buckets+0x890/0x890 [bcache]
[ 1158.504506]  ? kthread_park+0xb0/0xb0
[ 1158.504510]  ret_from_fork+0x35/0x40

Fix by making the call to bch_prio_write() non-blocking, so that
bch_allocator_thread() never waits on itself.

Moreover, make sure to wake up the garbage collector thread when
bch_prio_write() is failing to allocate buckets.

BugLink: https://bugs.launchpad.net/bugs/1784665
BugLink: https://bugs.launchpad.net/bugs/1796292


Signed-off-by: default avatarAndrea Righi <andrea.righi@canonical.com>
Signed-off-by: default avatarColy Li <colyli@suse.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 49e9a539

drivers/md/bcache/alloc.c

+4 −1
Original line number Diff line number Diff line
@@ -377,7 +377,10 @@ static int bch_allocator_thread(void *arg) 
			if (!fifo_full(&ca->free_inc))

				goto retry_invalidate;



			bch_prio_write(ca);

			if (bch_prio_write(ca, false) < 0) {

				ca->invalidate_needs_gc = 1;

				wake_up_gc(ca->set);

			}

		}

	}

out:

drivers/md/bcache/bcache.h

+1 −1
Original line number Diff line number Diff line
@@ -959,7 +959,7 @@ bool bch_cached_dev_error(struct cached_dev *dc); 
__printf(2, 3)

bool bch_cache_set_error(struct cache_set *c, const char *fmt, ...);



void bch_prio_write(struct cache *ca);

int bch_prio_write(struct cache *ca, bool wait);

void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent);



extern struct workqueue_struct *bcache_wq;

drivers/md/bcache/super.c

+21 −6
Original line number Diff line number Diff line
@@ -525,12 +525,29 @@ static void prio_io(struct cache *ca, uint64_t bucket, int op, 
	closure_sync(cl);

}



void bch_prio_write(struct cache *ca)

int bch_prio_write(struct cache *ca, bool wait)

{

	int i;

	struct bucket *b;

	struct closure cl;



	pr_debug("free_prio=%zu, free_none=%zu, free_inc=%zu",

		 fifo_used(&ca->free[RESERVE_PRIO]),

		 fifo_used(&ca->free[RESERVE_NONE]),

		 fifo_used(&ca->free_inc));



	/*

	 * Pre-check if there are enough free buckets. In the non-blocking

	 * scenario it's better to fail early rather than starting to allocate

	 * buckets and do a cleanup later in case of failure.

	 */

	if (!wait) {

		size_t avail = fifo_used(&ca->free[RESERVE_PRIO]) +

			       fifo_used(&ca->free[RESERVE_NONE]);

		if (prio_buckets(ca) > avail)

			return -ENOMEM;

	}



	closure_init_stack(&cl);



	lockdep_assert_held(&ca->set->bucket_lock);
@@ -540,9 +557,6 @@ void bch_prio_write(struct cache *ca) 
	atomic_long_add(ca->sb.bucket_size * prio_buckets(ca),

			&ca->meta_sectors_written);



	//pr_debug("free %zu, free_inc %zu, unused %zu", fifo_used(&ca->free),

	//	 fifo_used(&ca->free_inc), fifo_used(&ca->unused));



	for (i = prio_buckets(ca) - 1; i >= 0; --i) {

		long bucket;

		struct prio_set *p = ca->disk_buckets;
@@ -560,7 +574,7 @@ void bch_prio_write(struct cache *ca) 
		p->magic	= pset_magic(&ca->sb);

		p->csum		= bch_crc64(&p->magic, bucket_bytes(ca) - 8);



		bucket = bch_bucket_alloc(ca, RESERVE_PRIO, true);

		bucket = bch_bucket_alloc(ca, RESERVE_PRIO, wait);

		BUG_ON(bucket == -1);



		mutex_unlock(&ca->set->bucket_lock);
@@ -589,6 +603,7 @@ void bch_prio_write(struct cache *ca) 


		ca->prio_last_buckets[i] = ca->prio_buckets[i];

	}

	return 0;

}



static void prio_read(struct cache *ca, uint64_t bucket)
@@ -1884,7 +1899,7 @@ static int run_cache_set(struct cache_set *c) 


		mutex_lock(&c->bucket_lock);

		for_each_cache(ca, c, i)

			bch_prio_write(ca);

			bch_prio_write(ca, true);

		mutex_unlock(&c->bucket_lock);



		err = "cannot allocate new UUID bucket";