In order to avoid deadlocks due to bio queuing, discard and flush bios must be offloaded to a different thread.
writecache_flush_thread was not resistant to spurious wake-up, when it was woken up, it was assumed that wc->flush_bio is set. This patch reworks writecache_flush_thread so that it uses a list of bios and thus it is resistant to spurious wake-up. Signed-off-by: Mikulas Patocka <[email protected]> --- drivers/md/dm-writecache.c | 78 ++++++++++++++++++++++++++++----------------- 1 file changed, 50 insertions(+), 28 deletions(-) Index: linux-2.6/drivers/md/dm-writecache.c =================================================================== --- linux-2.6.orig/drivers/md/dm-writecache.c 2018-06-06 00:32:05.000000000 +0200 +++ linux-2.6/drivers/md/dm-writecache.c 2018-06-06 01:16:15.000000000 +0200 @@ -172,8 +172,7 @@ struct dm_writecache { struct task_struct *endio_thread; struct task_struct *flush_thread; - struct completion flush_completion; - struct bio *flush_bio; + struct bio_list flush_list; struct dm_kcopyd_client *dm_kcopyd; unsigned long *dirty_bitmap; @@ -1065,35 +1064,48 @@ static int writecache_flush_thread(void { struct dm_writecache *wc = data; - while (!kthread_should_stop()) { - struct bio *bio = wc->flush_bio; - - if (likely(bio)) { - if (bio_op(bio) == REQ_OP_DISCARD) - writecache_discard(wc, bio->bi_iter.bi_sector, bio_end_sector(bio)); - else - writecache_flush(wc); - } + while (1) { + struct bio *bio; + wc_lock(wc); + bio = bio_list_pop(&wc->flush_list); + if (bio) + goto process_bio; set_current_state(TASK_INTERRUPTIBLE); - /* for debugging - catch uninitialized use */ - wc->flush_bio = (void *)0x600 + POISON_POINTER_DELTA; - complete(&wc->flush_completion); + wc_unlock(wc); + + if (unlikely(kthread_should_stop())) { + set_current_state(TASK_RUNNING); + break; + } schedule(); - } - set_current_state(TASK_RUNNING); + continue; + +process_bio: + if (bio_op(bio) == REQ_OP_DISCARD) { + writecache_discard(wc, bio->bi_iter.bi_sector, bio_end_sector(bio)); + wc_unlock(wc); + bio_set_dev(bio, wc->dev->bdev); + generic_make_request(bio); + } else { + writecache_flush(wc); + wc_unlock(wc); + if (writecache_has_error(wc)) + bio->bi_status = BLK_STS_IOERR; + bio_endio(bio); + } + } return 0; } static void writecache_offload_bio(struct dm_writecache *wc, struct bio *bio) { - wc->flush_bio = bio; - reinit_completion(&wc->flush_completion); - wake_up_process(wc->flush_thread); - wait_for_completion_io(&wc->flush_completion); + if (bio_list_empty(&wc->flush_list)) + wake_up_process(wc->flush_thread); + bio_list_add(&wc->flush_list, bio); } static int writecache_map(struct dm_target *ti, struct bio *bio) @@ -1108,11 +1120,15 @@ static int writecache_map(struct dm_targ if (unlikely(bio->bi_opf & REQ_PREFLUSH)) { if (writecache_has_error(wc)) goto unlock_error; - if (WC_MODE_PMEM(wc)) + if (WC_MODE_PMEM(wc)) { writecache_flush(wc); - else + if (writecache_has_error(wc)) + goto unlock_error; + goto unlock_ok; + } else { writecache_offload_bio(wc, bio); - goto unlock_ok; + goto unlock_return; + } } bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector); @@ -1128,11 +1144,13 @@ static int writecache_map(struct dm_targ if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) { if (writecache_has_error(wc)) goto unlock_error; - if (WC_MODE_PMEM(wc)) + if (WC_MODE_PMEM(wc)) { writecache_discard(wc, bio->bi_iter.bi_sector, bio_end_sector(bio)); - else + goto unlock_remap_origin; + } else { writecache_offload_bio(wc, bio); - goto unlock_remap_origin; + goto unlock_return; + } } if (bio_data_dir(bio) == READ) { @@ -1224,6 +1242,10 @@ unlock_ok: bio_endio(bio); return DM_MAPIO_SUBMITTED; +unlock_return: + wc_unlock(wc); + return DM_MAPIO_SUBMITTED; + unlock_error: wc_unlock(wc); bio_io_error(bio); @@ -2017,7 +2039,7 @@ invalid_optional: size_t n_blocks, n_metadata_blocks; uint64_t n_bitmap_bits; - init_completion(&wc->flush_completion); + bio_list_init(&wc->flush_list); wc->flush_thread = kthread_create(writecache_flush_thread, wc, "dm_writecache_flush"); if (IS_ERR(wc->flush_thread)) { r = PTR_ERR(wc->flush_thread); @@ -2025,7 +2047,7 @@ invalid_optional: ti->error = "Couldn't spawn endio thread"; goto bad; } - writecache_offload_bio(wc, NULL); + wake_up_process(wc->flush_thread); r = calculate_memory_size(wc->memory_map_size, wc->block_size, &n_blocks, &n_metadata_blocks); -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
