From 8b64e881eb40ac8b9bfcbce068a97eef819044ee Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Fri, 20 Dec 2013 14:27:28 -0500 Subject: [PATCH] dm thin: fix set_pool_mode exposed pool operation races The pool mode must not be switched until after the corresponding pool process_* methods have been established. Otherwise, because set_pool_mode() isn't interlocked with the IO path for performance reasons, the IO path can end up executing process_* operations that don't match the mode. This patch eliminates problems like the following (as seen on really fast PCIe SSD storage when transitioning the pool's mode from PM_READ_ONLY to PM_WRITE): kernel: device-mapper: thin: 253:2: reached low water mark for data device: sending event. kernel: device-mapper: thin: 253:2: no free data space available. kernel: device-mapper: thin: 253:2: switching pool to read-only mode kernel: device-mapper: thin: 253:2: switching pool to write mode kernel: ------------[ cut here ]------------ kernel: WARNING: CPU: 11 PID: 7564 at drivers/md/dm-thin.c:995 handle_unserviceable_bio+0x146/0x160 [dm_thin_pool]() ... kernel: Workqueue: dm-thin do_worker [dm_thin_pool] kernel: 00000000000003e3 ffff880308831cc8 ffffffff8152ebcb 00000000000003e3 kernel: 0000000000000000 ffff880308831d08 ffffffff8104c46c ffff88032502a800 kernel: ffff880036409000 ffff88030ec7ce00 0000000000000001 00000000ffffffc3 kernel: Call Trace: kernel: [] dump_stack+0x49/0x5e kernel: [] warn_slowpath_common+0x8c/0xc0 kernel: [] warn_slowpath_null+0x1a/0x20 kernel: [] handle_unserviceable_bio+0x146/0x160 [dm_thin_pool] kernel: [] process_bio_read_only+0x136/0x180 [dm_thin_pool] kernel: [] process_deferred_bios+0xc5/0x230 [dm_thin_pool] kernel: [] do_worker+0x51/0x60 [dm_thin_pool] kernel: [] process_one_work+0x183/0x490 kernel: [] worker_thread+0x120/0x3a0 kernel: [] ? manage_workers+0x160/0x160 kernel: [] kthread+0xce/0xf0 kernel: [] ? kthread_freezable_should_stop+0x70/0x70 kernel: [] ret_from_fork+0x7c/0xb0 kernel: [] ? kthread_freezable_should_stop+0x70/0x70 kernel: ---[ end trace 3f00528e08ffa55c ]--- kernel: device-mapper: thin: pool mode is PM_WRITE not PM_READ_ONLY like expected!? dm-thin.c:995 was the WARN_ON_ONCE(get_pool_mode(pool) != PM_READ_ONLY); at the top of handle_unserviceable_bio(). And as the additional debugging I had conveys: the pool mode was _not_ PM_READ_ONLY like expected, it was already PM_WRITE, yet pool->process_bio was still set to process_bio_read_only(). Also, while fixing this up, reduce logging of redundant pool mode transitions by checking new_mode is different from old_mode. Signed-off-by: Mike Snitzer Cc: stable@vger.kernel.org --- drivers/md/dm-thin.c | 40 +++++++++++++++++++++++++++------------- 1 file changed, 27 insertions(+), 13 deletions(-) diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c index a55c5eb..d2328bb 100644 --- a/drivers/md/dm-thin.c +++ b/drivers/md/dm-thin.c @@ -1392,16 +1392,16 @@ static enum pool_mode get_pool_mode(struct pool *pool) return pool->pf.mode; } -static void set_pool_mode(struct pool *pool, enum pool_mode mode) +static void set_pool_mode(struct pool *pool, enum pool_mode new_mode) { int r; + enum pool_mode old_mode = pool->pf.mode; - pool->pf.mode = mode; - - switch (mode) { + switch (new_mode) { case PM_FAIL: - DMERR("%s: switching pool to failure mode", - dm_device_name(pool->pool_md)); + if (old_mode != new_mode) + DMERR("%s: switching pool to failure mode", + dm_device_name(pool->pool_md)); dm_pool_metadata_read_only(pool->pmd); pool->process_bio = process_bio_fail; pool->process_discard = process_bio_fail; @@ -1410,13 +1410,15 @@ static void set_pool_mode(struct pool *pool, enum pool_mode mode) break; case PM_READ_ONLY: - DMERR("%s: switching pool to read-only mode", - dm_device_name(pool->pool_md)); + if (old_mode != new_mode) + DMERR("%s: switching pool to read-only mode", + dm_device_name(pool->pool_md)); r = dm_pool_abort_metadata(pool->pmd); if (r) { DMERR("%s: aborting transaction failed", dm_device_name(pool->pool_md)); - set_pool_mode(pool, PM_FAIL); + new_mode = PM_FAIL; + set_pool_mode(pool, new_mode); } else { dm_pool_metadata_read_only(pool->pmd); pool->process_bio = process_bio_read_only; @@ -1427,6 +1429,9 @@ static void set_pool_mode(struct pool *pool, enum pool_mode mode) break; case PM_WRITE: + if (old_mode != new_mode) + DMINFO("%s: switching pool to write mode", + dm_device_name(pool->pool_md)); dm_pool_metadata_read_write(pool->pmd); pool->process_bio = process_bio; pool->process_discard = process_discard; @@ -1434,6 +1439,8 @@ static void set_pool_mode(struct pool *pool, enum pool_mode mode) pool->process_prepared_discard = process_prepared_discard; break; } + + pool->pf.mode = new_mode; } /* @@ -1677,6 +1684,17 @@ static int bind_control_target(struct pool *pool, struct dm_target *ti) enum pool_mode new_mode = pt->adjusted_pf.mode; /* + * Don't change the pool's mode until set_pool_mode() below. + * Otherwise the pool's process_* function pointers may + * not match the desired pool mode. + */ + pt->adjusted_pf.mode = old_mode; + + pool->ti = ti; + pool->pf = pt->adjusted_pf; + pool->low_water_blocks = pt->low_water_blocks; + + /* * If we were in PM_FAIL mode, rollback of metadata failed. We're * not going to recover without a thin_repair. So we never let the * pool move out of the old mode. On the other hand a PM_READ_ONLY @@ -1686,10 +1704,6 @@ static int bind_control_target(struct pool *pool, struct dm_target *ti) if (old_mode == PM_FAIL) new_mode = old_mode; - pool->ti = ti; - pool->low_water_blocks = pt->low_water_blocks; - pool->pf = pt->adjusted_pf; - set_pool_mode(pool, new_mode); return 0; -- 2.7.4