[PATCH] bcache: add separate workqueue for journal_write to avoid deadlock
From: guoju
Date: Thu Sep 27 2018 - 09:46:23 EST
After write SSD completed, bcache schedule journal_write work to
system_wq, that 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 <fangguoju@xxxxxxxxx>
---
drivers/md/bcache/bcache.h | 1 +
drivers/md/bcache/journal.c | 6 +++---
drivers/md/bcache/super.c | 8 ++++++++
3 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 83504dd..954dad2 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -965,6 +965,7 @@ bool bch_alloc_sectors(struct cache_set *c, struct bkey *k,
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 6116bbf..522c742 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 3ede144..64715a8 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -47,6 +47,7 @@
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 */
@@ -2344,6 +2345,9 @@ 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);
@@ -2373,6 +2377,10 @@ 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;
--
1.8.3.1