| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.19 22/75] bcache: only set BCACHE_DEV_WB_RUNNING when cached device attached | Date | Mon, 17 Jun 2019 23:09:33 +0200 |
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From: Coly Li <colyli@suse.de>
commit 1f0ffa67349c56ea54c03ccfd1e073c990e7411e upstream.
When people set a writeback percent via sysfs file, /sys/block/bcache<N>/bcache/writeback_percent current code directly sets BCACHE_DEV_WB_RUNNING to dc->disk.flags and schedules kworker dc->writeback_rate_update.
If there is no cache set attached to, the writeback kernel thread is not running indeed, running dc->writeback_rate_update does not make sense and may cause NULL pointer deference when reference cache set pointer inside update_writeback_rate().
This patch checks whether the cache set point (dc->disk.c) is NULL in sysfs interface handler, and only set BCACHE_DEV_WB_RUNNING and schedule dc->writeback_rate_update when dc->disk.c is not NULL (it means the cache device is attached to a cache set).
This problem might be introduced from initial bcache commit, but commit 3fd47bfe55b0 ("bcache: stop dc->writeback_rate_update properly") changes part of the original code piece, so I add 'Fixes: 3fd47bfe55b0' to indicate from which commit this patch can be applied.
Fixes: 3fd47bfe55b0 ("bcache: stop dc->writeback_rate_update properly") Reported-by: Bjørn Forsman <bjorn.forsman@gmail.com> Signed-off-by: Coly Li <colyli@suse.de> Reviewed-by: Bjørn Forsman <bjorn.forsman@gmail.com> Cc: stable@vger.kernel.org Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- drivers/md/bcache/sysfs.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
--- a/drivers/md/bcache/sysfs.c +++ b/drivers/md/bcache/sysfs.c @@ -393,8 +393,13 @@ STORE(bch_cached_dev) if (attr == &sysfs_writeback_running) bch_writeback_queue(dc); + /* + * Only set BCACHE_DEV_WB_RUNNING when cached device attached to + * a cache set, otherwise it doesn't make sense. + */ if (attr == &sysfs_writeback_percent) - if (!test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)) + if ((dc->disk.c != NULL) && + (!test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags))) schedule_delayed_work(&dc->writeback_rate_update, dc->writeback_rate_update_seconds * HZ);
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