[PATCH 4.4 63/66] bcache: fix for gc and write-back race

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

--

From: Tang Junhui 

commit 9baf30972b5568d8b5bc8b3c46a6ec5b58100463 upstream.

gc and write-back get raced (see the email "bcache get stucked" I sended
before):
gc thread   write-back thread
|   |bch_writeback_thread()
|bch_gc_thread()|
|   |==>read_dirty()
|==>bch_btree_gc()  |
|==>btree_root() //get btree root   |
|//node write locker|
|==>bch_btree_gc_root() |
|   |==>read_dirty_submit()
|   |==>write_dirty()
|   |==>continue_at(cl,
|   |   write_dirty_finish,
|   |   system_wq);
|   |==>write_dirty_finish()//excute
|   |   //in system_wq
|   |==>bch_btree_insert()
|   |==>bch_btree_map_leaf_nodes()
|   |==>__bch_btree_map_nodes()
|   |==>btree_root //try to get btree
|   |  //root node read
|   |  //lock
|   |-stuck here
|==>bch_btree_set_root()
|==>bch_journal_meta()
|==>bch_journal()
|==>journal_try_write()
|==>journal_write_unlocked() //journal_full(>journal)
|//condition satisfied
|==>continue_at(cl, journal_write, system_wq); //try to excute
|   //journal_write in system_wq
|   //but work queue is excuting
|   //write_dirty_finish()
|==>closure_sync(); //wait journal_write execute
|   //over and wake up gc,
|-stuck here
|==>release root node write locker

This patch alloc a separate work-queue for write-back thread to avoid such
race.

(Commit log re-organized by Coly Li to pass checkpatch.pl checking)

Signed-off-by: Tang Junhui 
Acked-by: Coly Li 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman 

---
 drivers/md/bcache/bcache.h|1 +
 drivers/md/bcache/super.c |2 ++
 drivers/md/bcache/writeback.c |9 +++--
 3 files changed, 10 insertions(+), 2 deletions(-)

--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -333,6 +333,7 @@ struct cached_dev {
/* Limit number of writeback bios in flight */
struct semaphorein_flight;
struct task_struct  *writeback_thread;
+   struct workqueue_struct *writeback_write_wq;
 
struct keybuf   writeback_keys;
 
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1056,6 +1056,8 @@ static void cached_dev_free(struct closu
cancel_delayed_work_sync(>writeback_rate_update);
if (!IS_ERR_OR_NULL(dc->writeback_thread))
kthread_stop(dc->writeback_thread);
+   if (dc->writeback_write_wq)
+   destroy_workqueue(dc->writeback_write_wq);
 
mutex_lock(_register_lock);
 
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -191,7 +191,7 @@ static void write_dirty(struct closure *
 
closure_bio_submit(>bio, cl);
 
-   continue_at(cl, write_dirty_finish, system_wq);
+   continue_at(cl, write_dirty_finish, io->dc->writeback_write_wq);
 }
 
 static void read_dirty_endio(struct bio *bio)
@@ -211,7 +211,7 @@ static void read_dirty_submit(struct clo
 
closure_bio_submit(>bio, cl);
 
-   continue_at(cl, write_dirty, system_wq);
+   continue_at(cl, write_dirty, io->dc->writeback_write_wq);
 }
 
 static void read_dirty(struct cached_dev *dc)
@@ -523,6 +523,11 @@ void bch_cached_dev_writeback_init(struc
 
 int bch_cached_dev_writeback_start(struct cached_dev *dc)
 {
+   dc->writeback_write_wq = alloc_workqueue("bcache_writeback_wq",
+   WQ_MEM_RECLAIM, 0);
+   if (!dc->writeback_write_wq)
+   return -ENOMEM;
+
dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
  "bcache_writeback");
if (IS_ERR(dc->writeback_thread))

[PATCH 4.4 63/66] bcache: fix for gc and write-back race

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

--

From: Tang Junhui 

commit 9baf30972b5568d8b5bc8b3c46a6ec5b58100463 upstream.

gc and write-back get raced (see the email "bcache get stucked" I sended
before):
gc thread   write-back thread
|   |bch_writeback_thread()
|bch_gc_thread()|
|   |==>read_dirty()
|==>bch_btree_gc()  |
|==>btree_root() //get btree root   |
|//node write locker|
|==>bch_btree_gc_root() |
|   |==>read_dirty_submit()
|   |==>write_dirty()
|   |==>continue_at(cl,
|   |   write_dirty_finish,
|   |   system_wq);
|   |==>write_dirty_finish()//excute
|   |   //in system_wq
|   |==>bch_btree_insert()
|   |==>bch_btree_map_leaf_nodes()
|   |==>__bch_btree_map_nodes()
|   |==>btree_root //try to get btree
|   |  //root node read
|   |  //lock
|   |-stuck here
|==>bch_btree_set_root()
|==>bch_journal_meta()
|==>bch_journal()
|==>journal_try_write()
|==>journal_write_unlocked() //journal_full(>journal)
|//condition satisfied
|==>continue_at(cl, journal_write, system_wq); //try to excute
|   //journal_write in system_wq
|   //but work queue is excuting
|   //write_dirty_finish()
|==>closure_sync(); //wait journal_write execute
|   //over and wake up gc,
|-stuck here
|==>release root node write locker

This patch alloc a separate work-queue for write-back thread to avoid such
race.

(Commit log re-organized by Coly Li to pass checkpatch.pl checking)

Signed-off-by: Tang Junhui 
Acked-by: Coly Li 
Signed-off-by: Jens Axboe 
Signed-off-by: Greg Kroah-Hartman 

---
 drivers/md/bcache/bcache.h|1 +
 drivers/md/bcache/super.c |2 ++
 drivers/md/bcache/writeback.c |9 +++--
 3 files changed, 10 insertions(+), 2 deletions(-)

--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -333,6 +333,7 @@ struct cached_dev {
/* Limit number of writeback bios in flight */
struct semaphorein_flight;
struct task_struct  *writeback_thread;
+   struct workqueue_struct *writeback_write_wq;
 
struct keybuf   writeback_keys;
 
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1056,6 +1056,8 @@ static void cached_dev_free(struct closu
cancel_delayed_work_sync(>writeback_rate_update);
if (!IS_ERR_OR_NULL(dc->writeback_thread))
kthread_stop(dc->writeback_thread);
+   if (dc->writeback_write_wq)
+   destroy_workqueue(dc->writeback_write_wq);
 
mutex_lock(_register_lock);
 
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -191,7 +191,7 @@ static void write_dirty(struct closure *
 
closure_bio_submit(>bio, cl);
 
-   continue_at(cl, write_dirty_finish, system_wq);
+   continue_at(cl, write_dirty_finish, io->dc->writeback_write_wq);
 }
 
 static void read_dirty_endio(struct bio *bio)
@@ -211,7 +211,7 @@ static void read_dirty_submit(struct clo
 
closure_bio_submit(>bio, cl);
 
-   continue_at(cl, write_dirty, system_wq);
+   continue_at(cl, write_dirty, io->dc->writeback_write_wq);
 }
 
 static void read_dirty(struct cached_dev *dc)
@@ -523,6 +523,11 @@ void bch_cached_dev_writeback_init(struc
 
 int bch_cached_dev_writeback_start(struct cached_dev *dc)
 {
+   dc->writeback_write_wq = alloc_workqueue("bcache_writeback_wq",
+   WQ_MEM_RECLAIM, 0);
+   if (!dc->writeback_write_wq)
+   return -ENOMEM;
+
dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
  "bcache_writeback");
if (IS_ERR(dc->writeback_thread))