diff options
author | Coly Li | 2018-03-18 17:36:16 -0700 |
---|---|---|
committer | Jens Axboe | 2018-03-18 20:15:20 -0600 |
commit | 3fd47bfe55b00d5ac7b0a44c9301c07be39b1082 (patch) | |
tree | 32270c555e9f87fc2b4da0e7596ddbb0264d644e /drivers/md | |
parent | fadd94e05c02afec7b70b0b14915624f1782f578 (diff) |
bcache: stop dc->writeback_rate_update properly
struct delayed_work writeback_rate_update in struct cache_dev is a delayed
worker to call function update_writeback_rate() in period (the interval is
defined by dc->writeback_rate_update_seconds).
When a metadate I/O error happens on cache device, bcache error handling
routine bch_cache_set_error() will call bch_cache_set_unregister() to
retire whole cache set. On the unregister code path, this delayed work is
stopped by calling cancel_delayed_work_sync(&dc->writeback_rate_update).
dc->writeback_rate_update is a special delayed work from others in bcache.
In its routine update_writeback_rate(), this delayed work is re-armed
itself. That means when cancel_delayed_work_sync() returns, this delayed
work can still be executed after several seconds defined by
dc->writeback_rate_update_seconds.
The problem is, after cancel_delayed_work_sync() returns, the cache set
unregister code path will continue and release memory of struct cache set.
Then the delayed work is scheduled to run, __update_writeback_rate()
will reference the already released cache_set memory, and trigger a NULL
pointer deference fault.
This patch introduces two more bcache device flags,
- BCACHE_DEV_WB_RUNNING
bit set: bcache device is in writeback mode and running, it is OK for
dc->writeback_rate_update to re-arm itself.
bit clear:bcache device is trying to stop dc->writeback_rate_update,
this delayed work should not re-arm itself and quit.
- BCACHE_DEV_RATE_DW_RUNNING
bit set: routine update_writeback_rate() is executing.
bit clear: routine update_writeback_rate() quits.
This patch also adds a function cancel_writeback_rate_update_dwork() to
wait for dc->writeback_rate_update quits before cancel it by calling
cancel_delayed_work_sync(). In order to avoid a deadlock by unexpected
quit dc->writeback_rate_update, after time_out seconds this function will
give up and continue to call cancel_delayed_work_sync().
And here I explain how this patch stops self re-armed delayed work properly
with the above stuffs.
update_writeback_rate() sets BCACHE_DEV_RATE_DW_RUNNING at its beginning
and clears BCACHE_DEV_RATE_DW_RUNNING at its end. Before calling
cancel_writeback_rate_update_dwork() clear flag BCACHE_DEV_WB_RUNNING.
Before calling cancel_delayed_work_sync() wait utill flag
BCACHE_DEV_RATE_DW_RUNNING is clear. So when calling
cancel_delayed_work_sync(), dc->writeback_rate_update must be already re-
armed, or quite by seeing BCACHE_DEV_WB_RUNNING cleared. In both cases
delayed work routine update_writeback_rate() won't be executed after
cancel_delayed_work_sync() returns.
Inside update_writeback_rate() before calling schedule_delayed_work(), flag
BCACHE_DEV_WB_RUNNING is checked before. If this flag is cleared, it means
someone is about to stop the delayed work. Because flag
BCACHE_DEV_RATE_DW_RUNNING is set already and cancel_delayed_work_sync()
has to wait for this flag to be cleared, we don't need to worry about race
condition here.
If update_writeback_rate() is scheduled to run after checking
BCACHE_DEV_RATE_DW_RUNNING and before calling cancel_delayed_work_sync()
in cancel_writeback_rate_update_dwork(), it is also safe. Because at this
moment BCACHE_DEV_WB_RUNNING is cleared with memory barrier. As I mentioned
previously, update_writeback_rate() will see BCACHE_DEV_WB_RUNNING is clear
and quit immediately.
Because there are more dependences inside update_writeback_rate() to struct
cache_set memory, dc->writeback_rate_update is not a simple self re-arm
delayed work. After trying many different methods (e.g. hold dc->count, or
use locks), this is the only way I can find which works to properly stop
dc->writeback_rate_update delayed work.
Changelog:
v3: change values of BCACHE_DEV_WB_RUNNING and BCACHE_DEV_RATE_DW_RUNNING
to bit index, for test_bit().
v2: Try to fix the race issue which is pointed out by Junhui.
v1: The initial version for review
Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Junhui Tang <tang.junhui@zte.com.cn>
Reviewed-by: Michael Lyle <mlyle@lyle.org>
Cc: Michael Lyle <mlyle@lyle.org>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/md')
-rw-r--r-- | drivers/md/bcache/bcache.h | 9 | ||||
-rw-r--r-- | drivers/md/bcache/super.c | 38 | ||||
-rw-r--r-- | drivers/md/bcache/sysfs.c | 3 | ||||
-rw-r--r-- | drivers/md/bcache/writeback.c | 29 |
4 files changed, 69 insertions, 10 deletions
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h index 12e5197f186c..b5ddb848cd31 100644 --- a/drivers/md/bcache/bcache.h +++ b/drivers/md/bcache/bcache.h @@ -258,10 +258,11 @@ struct bcache_device { struct gendisk *disk; unsigned long flags; -#define BCACHE_DEV_CLOSING 0 -#define BCACHE_DEV_DETACHING 1 -#define BCACHE_DEV_UNLINK_DONE 2 - +#define BCACHE_DEV_CLOSING 0 +#define BCACHE_DEV_DETACHING 1 +#define BCACHE_DEV_UNLINK_DONE 2 +#define BCACHE_DEV_WB_RUNNING 3 +#define BCACHE_DEV_RATE_DW_RUNNING 4 unsigned nr_stripes; unsigned stripe_size; atomic_t *stripe_sectors_dirty; diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index 020be4f1cd8b..e5be599338c5 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -899,6 +899,31 @@ void bch_cached_dev_run(struct cached_dev *dc) pr_debug("error creating sysfs link"); } +/* + * If BCACHE_DEV_RATE_DW_RUNNING is set, it means routine of the delayed + * work dc->writeback_rate_update is running. Wait until the routine + * quits (BCACHE_DEV_RATE_DW_RUNNING is clear), then continue to + * cancel it. If BCACHE_DEV_RATE_DW_RUNNING is not clear after time_out + * seconds, give up waiting here and continue to cancel it too. + */ +static void cancel_writeback_rate_update_dwork(struct cached_dev *dc) +{ + int time_out = WRITEBACK_RATE_UPDATE_SECS_MAX * HZ; + + do { + if (!test_bit(BCACHE_DEV_RATE_DW_RUNNING, + &dc->disk.flags)) + break; + time_out--; + schedule_timeout_interruptible(1); + } while (time_out > 0); + + if (time_out == 0) + pr_warn("give up waiting for dc->writeback_write_update to quit"); + + cancel_delayed_work_sync(&dc->writeback_rate_update); +} + static void cached_dev_detach_finish(struct work_struct *w) { struct cached_dev *dc = container_of(w, struct cached_dev, detach); @@ -911,7 +936,9 @@ static void cached_dev_detach_finish(struct work_struct *w) mutex_lock(&bch_register_lock); - cancel_delayed_work_sync(&dc->writeback_rate_update); + if (test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)) + cancel_writeback_rate_update_dwork(dc); + if (!IS_ERR_OR_NULL(dc->writeback_thread)) { kthread_stop(dc->writeback_thread); dc->writeback_thread = NULL; @@ -954,6 +981,7 @@ void bch_cached_dev_detach(struct cached_dev *dc) closure_get(&dc->disk.cl); bch_writeback_queue(dc); + cached_dev_put(dc); } @@ -1081,14 +1109,16 @@ static void cached_dev_free(struct closure *cl) { struct cached_dev *dc = container_of(cl, struct cached_dev, disk.cl); - cancel_delayed_work_sync(&dc->writeback_rate_update); + mutex_lock(&bch_register_lock); + + if (test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)) + cancel_writeback_rate_update_dwork(dc); + 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); - if (atomic_read(&dc->running)) bd_unlink_disk_holder(dc->bdev, dc->disk.disk); bcache_device_free(&dc->disk); diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c index 78cd7bd50fdd..55673508628f 100644 --- a/drivers/md/bcache/sysfs.c +++ b/drivers/md/bcache/sysfs.c @@ -309,7 +309,8 @@ STORE(bch_cached_dev) bch_writeback_queue(dc); if (attr == &sysfs_writeback_percent) - schedule_delayed_work(&dc->writeback_rate_update, + if (!test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)) + schedule_delayed_work(&dc->writeback_rate_update, dc->writeback_rate_update_seconds * HZ); mutex_unlock(&bch_register_lock); diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 4dbeaaa575bf..8f98ef1038d3 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -115,6 +115,21 @@ static void update_writeback_rate(struct work_struct *work) struct cached_dev, writeback_rate_update); + /* + * should check BCACHE_DEV_RATE_DW_RUNNING before calling + * cancel_delayed_work_sync(). + */ + set_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags); + /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */ + smp_mb(); + + if (!test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)) { + clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags); + /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */ + smp_mb(); + return; + } + down_read(&dc->writeback_lock); if (atomic_read(&dc->has_dirty) && @@ -123,8 +138,18 @@ static void update_writeback_rate(struct work_struct *work) up_read(&dc->writeback_lock); - schedule_delayed_work(&dc->writeback_rate_update, + if (test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)) { + schedule_delayed_work(&dc->writeback_rate_update, dc->writeback_rate_update_seconds * HZ); + } + + /* + * should check BCACHE_DEV_RATE_DW_RUNNING before calling + * cancel_delayed_work_sync(). + */ + clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags); + /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */ + smp_mb(); } static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors) @@ -675,6 +700,7 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc) dc->writeback_rate_p_term_inverse = 40; dc->writeback_rate_i_term_inverse = 10000; + WARN_ON(test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)); INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate); } @@ -693,6 +719,7 @@ int bch_cached_dev_writeback_start(struct cached_dev *dc) return PTR_ERR(dc->writeback_thread); } + WARN_ON(test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)); schedule_delayed_work(&dc->writeback_rate_update, dc->writeback_rate_update_seconds * HZ); |