Re: [PATCH -next v3] md/raid5-cache: fix a deadlock in r5l_exit_log()
From: Song Liu <song@kernel.org>
Date: 2023-07-29 10:45:10
Also in:
lkml
On Sat, Jul 8, 2023 at 5:19 PM Yu Kuai [off-list ref] wrote:
From: Yu Kuai <redacted>
Commit b13015af94cf ("md/raid5-cache: Clear conf->log after finishing
work") introduce a new problem:
// caller hold reconfig_mutex
r5l_exit_log
flush_work(&log->disable_writeback_work)
r5c_disable_writeback_async
wait_event
/*
* conf->log is not NULL, and mddev_trylock()
* will fail, wait_event() can never pass.
*/
conf->log = NULL
Fix this problem by setting 'config->log' to NULL before wake_up() as it
used to be, so that wait_event() from r5c_disable_writeback_async() can
exist. In the meantime, move forward md_unregister_thread() so that
null-ptr-deref this commit fixed can still be fixed.
Fixes: b13015af94cf ("md/raid5-cache: Clear conf->log after finishing work")
Signed-off-by: Yu Kuai <redacted>Applied to md-next. Thanks! Song
quoted hunk ↗ jump to hunk
--- Changes in v3: - Use a different solution. drivers/md/raid5-cache.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c index 47ba7d9e81e1..2eac4a50d99b 100644 --- a/drivers/md/raid5-cache.c +++ b/drivers/md/raid5-cache.c@@ -3168,12 +3168,15 @@ void r5l_exit_log(struct r5conf *conf) { struct r5l_log *log = conf->log; - /* Ensure disable_writeback_work wakes up and exits */ - wake_up(&conf->mddev->sb_wait); - flush_work(&log->disable_writeback_work); md_unregister_thread(&log->reclaim_thread); + /* + * 'reconfig_mutex' is held by caller, set 'confg->log' to NULL to + * ensure disable_writeback_work wakes up and exits. + */ conf->log = NULL; + wake_up(&conf->mddev->sb_wait); + flush_work(&log->disable_writeback_work); mempool_exit(&log->meta_pool); bioset_exit(&log->bs); --2.39.2