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, cached_dev_free() calls cancel_delayed_work_sync(&dc->writeback_rate_update) to stop this delayed work. 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 after a piece of time. 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 eventually release memory of struct cache set. Then the delayed work is scheduled to run, and inside its routine update_writeback_rate() that already released cache set NULL pointer will be accessed. Now a NULL pointer deference panic is triggered. In order to avoid the above problem, this patch checks cache set flags in delayed work routine update_writeback_rate(). If flag CACHE_SET_STOPPING is set, this routine will quit without re-arm the delayed work. Then the NULL pointer deference panic won't happen after cache set is released. Signed-off-by: Coly Li <colyli@xxxxxxx> --- drivers/md/bcache/writeback.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 0789a9e18337..745d9b2a326f 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -91,6 +91,11 @@ static void update_writeback_rate(struct work_struct *work) struct cached_dev *dc = container_of(to_delayed_work(work), struct cached_dev, writeback_rate_update); + struct cache_set *c = dc->disk.c; + + /* quit directly if cache set is stopping */ + if (test_bit(CACHE_SET_STOPPING, &c->flags)) + return; down_read(&dc->writeback_lock); @@ -100,6 +105,10 @@ static void update_writeback_rate(struct work_struct *work) up_read(&dc->writeback_lock); + /* do not schedule delayed work if cache set is stopping */ + if (test_bit(CACHE_SET_STOPPING, &c->flags)) + return; + schedule_delayed_work(&dc->writeback_rate_update, dc->writeback_rate_update_seconds * HZ); } -- 2.15.1
