The patch below does not apply to the 4.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 0f843e65d9eef4936929bb036c5f771fb261eea4 Mon Sep 17 00:00:00 2001

From: Guoju Fang fangguoju@gmail.com Date: Thu, 27 Sep 2018 23:41:46 +0800 Subject: [PATCH] bcache: add separate workqueue for journal_write to avoid deadlock

After write SSD completed, bcache schedules journal_write work to system_wq, which is a public workqueue in system, without WQ_MEM_RECLAIM flag. system_wq is also a bound wq, and there may be no idle kworker on current processor. Creating a new kworker may unfortunately need to reclaim memory first, by shrinking cache and slab used by vfs, which depends on bcache device. That's a deadlock.

This patch create a new workqueue for journal_write with WQ_MEM_RECLAIM flag. It's rescuer thread will work to avoid the deadlock.

Signed-off-by: Guoju Fang fangguoju@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Coly Li colyli@suse.de Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h index 83504dd8100a..954dad29e6e8 100644 --- a/drivers/md/bcache/bcache.h +++ b/drivers/md/bcache/bcache.h @@ -965,6 +965,7 @@ void bch_prio_write(struct cache *ca); void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent);

extern struct workqueue_struct *bcache_wq; +extern struct workqueue_struct *bch_journal_wq; extern struct mutex bch_register_lock; extern struct list_head bch_cache_sets;

diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c index 6116bbf870d8..522c7426f3a0 100644 --- a/drivers/md/bcache/journal.c +++ b/drivers/md/bcache/journal.c @@ -485,7 +485,7 @@ static void do_journal_discard(struct cache *ca)

closure_get(&ca->set->cl); INIT_WORK(&ja->discard_work, journal_discard_work); - schedule_work(&ja->discard_work); + queue_work(bch_journal_wq, &ja->discard_work); } }

@@ -592,7 +592,7 @@ static void journal_write_done(struct closure *cl) : &j->w[0];

__closure_wake_up(&w->wait); - continue_at_nobarrier(cl, journal_write, system_wq); + continue_at_nobarrier(cl, journal_write, bch_journal_wq); }

static void journal_write_unlock(struct closure *cl) @@ -627,7 +627,7 @@ static void journal_write_unlocked(struct closure *cl) spin_unlock(&c->journal.lock);

btree_flush_write(c); - continue_at(cl, journal_write, system_wq); + continue_at(cl, journal_write, bch_journal_wq); return; }

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index 94c756c66bd7..30ba9aeb5ee8 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -47,6 +47,7 @@ static int bcache_major; static DEFINE_IDA(bcache_device_idx); static wait_queue_head_t unregister_wait; struct workqueue_struct *bcache_wq; +struct workqueue_struct *bch_journal_wq;

#define BTREE_MAX_PAGES (256 * 1024 / PAGE_SIZE) /* limitation of partitions number on single bcache device */ @@ -2341,6 +2342,9 @@ static void bcache_exit(void) kobject_put(bcache_kobj); if (bcache_wq) destroy_workqueue(bcache_wq); + if (bch_journal_wq) + destroy_workqueue(bch_journal_wq); + if (bcache_major) unregister_blkdev(bcache_major, "bcache"); unregister_reboot_notifier(&reboot); @@ -2370,6 +2374,10 @@ static int __init bcache_init(void) if (!bcache_wq) goto err;

+ bch_journal_wq = alloc_workqueue("bch_journal", WQ_MEM_RECLAIM, 0); + if (!bch_journal_wq) + goto err; + bcache_kobj = kobject_create_and_add("bcache", fs_kobj); if (!bcache_kobj) goto err;