[PATCH 3.11 089/233] dm thin: fix set_pool_mode exposed pool operation races

From: Luis Henriques
Date: Fri Feb 07 2014 - 06:50:08 EST -stable review patch. If anyone has any objections, please let me know.


From: Mike Snitzer <snitzer@xxxxxxxxxx>

commit 8b64e881eb40ac8b9bfcbce068a97eef819044ee upstream.

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: [<ffffffff8152ebcb>] dump_stack+0x49/0x5e
kernel: [<ffffffff8104c46c>] warn_slowpath_common+0x8c/0xc0
kernel: [<ffffffff8104c4ba>] warn_slowpath_null+0x1a/0x20
kernel: [<ffffffffa001e2c6>] handle_unserviceable_bio+0x146/0x160 [dm_thin_pool]
kernel: [<ffffffffa001f276>] process_bio_read_only+0x136/0x180 [dm_thin_pool]
kernel: [<ffffffffa0020b75>] process_deferred_bios+0xc5/0x230 [dm_thin_pool]
kernel: [<ffffffffa0020d31>] do_worker+0x51/0x60 [dm_thin_pool]
kernel: [<ffffffff81067823>] process_one_work+0x183/0x490
kernel: [<ffffffff81068c70>] worker_thread+0x120/0x3a0
kernel: [<ffffffff81068b50>] ? manage_workers+0x160/0x160
kernel: [<ffffffff8106e86e>] kthread+0xce/0xf0
kernel: [<ffffffff8106e7a0>] ? kthread_freezable_should_stop+0x70/0x70
kernel: [<ffffffff8153b3ec>] ret_from_fork+0x7c/0xb0
kernel: [<ffffffff8106e7a0>] ? 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 <snitzer@xxxxxxxxxx>
[ luis: backported to 3.11: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
drivers/md/dm-thin.c | 41 +++++++++++++++++++++++++++++------------
1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 18a9b12..0a9b087 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1387,15 +1387,16 @@ 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("switching pool to failure mode");
+ if (old_mode != new_mode)
+ DMERR("%s: switching pool to failure mode",
+ dm_device_name(pool->pool_md));
pool->process_bio = process_bio_fail;
pool->process_discard = process_bio_fail;
@@ -1404,11 +1405,15 @@ static void set_pool_mode(struct pool *pool, enum pool_mode mode)

- DMERR("switching pool to read-only mode");
+ 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("aborting transaction failed");
- set_pool_mode(pool, PM_FAIL);
+ DMERR("%s: aborting transaction failed",
+ dm_device_name(pool->pool_md));
+ new_mode = PM_FAIL;
+ set_pool_mode(pool, new_mode);
} else {
pool->process_bio = process_bio_read_only;
@@ -1419,6 +1424,9 @@ static void set_pool_mode(struct pool *pool, enum pool_mode mode)

case PM_WRITE:
+ if (old_mode != new_mode)
+ DMINFO("%s: switching pool to write mode",
+ dm_device_name(pool->pool_md));
pool->process_bio = process_bio;
pool->process_discard = process_discard;
@@ -1426,6 +1434,8 @@ static void set_pool_mode(struct pool *pool, enum pool_mode mode)
pool->process_prepared_discard = process_prepared_discard;
+ pool->pf.mode = new_mode;

@@ -1642,6 +1652,17 @@ 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
@@ -1651,10 +1672,6 @@ 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;

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