A NULL pointer dereferlence on conf->log is seen randomly with the mdadm test 21raid5cache. Kasan reporst: BUG: KASAN: null-ptr-deref in r5l_reclaimable_space+0xf5/0x140 Read of size 8 at addr 0000000000000860 by task md0_reclaim/3086 Call Trace: dump_stack_lvl+0x5a/0x74 kasan_report.cold+0x5f/0x1a9 __asan_load8+0x69/0x90 r5l_reclaimable_space+0xf5/0x140 r5l_do_reclaim+0xf4/0x5e0 r5l_reclaim_thread+0x69/0x3b0 md_thread+0x1a2/0x2c0 kthread+0x177/0x1b0 ret_from_fork+0x22/0x30 This is caused by conf->log being cleared in r5l_exit_log() before stopping the reclaim thread. To fix this, clear conf->log after the reclaim_thread is unregistered and after flushing disable_writeback_work. Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx> --- drivers/md/raid5-cache.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c index 48020d36b334..d6461d4814ab 100644 --- a/drivers/md/raid5-cache.c +++ b/drivers/md/raid5-cache.c @@ -3167,12 +3167,13 @@ void r5l_exit_log(struct r5conf *conf) lockdep_assert_held(&conf->mddev->reconfig_mutex); - conf->log = NULL; - /* 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); + + conf->log = NULL; + mempool_exit(&log->meta_pool); bioset_exit(&log->bs); mempool_exit(&log->io_pool); -- 2.30.2
