bcache: fix for gc and write-back race
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(&c->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 <[email protected]>
Acked-by: Coly Li <[email protected]>
Cc: [email protected]
Signed-off-by: Jens Axboe <[email protected]>
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index dee542f..2ed9bd2 100644
--- 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 semaphore in_flight;
struct task_struct *writeback_thread;
+ struct workqueue_struct *writeback_write_wq;
struct keybuf writeback_keys;
