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Commit 50aee960 authored by Tang Junhui's avatar Tang Junhui Committed by Greg Kroah-Hartman
Browse files

bcache: fix for gc and write-back race 



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: default avatarTang Junhui <tang.junhui@zte.com.cn>
Acked-by: default avatarColy Li <colyli@suse.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent c04dc907

drivers/md/bcache/bcache.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

drivers/md/bcache/super.c

+2 −0
Original line number Diff line number Diff line
@@ -1087,6 +1087,8 @@ static void cached_dev_free(struct closure *cl) 
	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);

drivers/md/bcache/writeback.c

+7 −2
Original line number Diff line number Diff line
@@ -191,7 +191,7 @@ static void write_dirty(struct closure *cl) 


	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 closure *cl) 


	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(struct cached_dev *dc) 


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))