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Subject[PATCH v4 07/11] md/raid5-cache: Clear conf->log after finishing work
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@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
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 b1fc65e113f8..ca57b5fac599 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -3165,12 +3165,13 @@ void r5l_exit_log(struct r5conf *conf)
{
struct r5l_log *log = conf->log;

- 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
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