3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tang Junhui <tang.junhui@xxxxxxxxxx> 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(&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 <tang.junhui@xxxxxxxxxx> Acked-by: Coly Li <colyli@xxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -348,6 +348,7 @@ 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; --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -1087,6 +1087,8 @@ static void cached_dev_free(struct closu cancel_delayed_work_sync(&dc->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(&bch_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(&io->bio, cl, &io->dc->disk); - 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, int error) @@ -211,7 +211,7 @@ static void read_dirty_submit(struct clo closure_bio_submit(&io->bio, cl, &io->dc->disk); - 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))