The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

Thanks, Sasha

------------------ original commit in Linus's tree ------------------

From 6e7132ed3c07bd8a6ce3db4bb307ef2852b322dc Mon Sep 17 00:00:00 2001 From: Mikulas Patocka mpatocka@redhat.com Date: Wed, 20 Mar 2024 18:43:11 +0100 Subject: [PATCH] dm snapshot: fix lockup in dm_exception_table_exit

There was reported lockup when we exit a snapshot with many exceptions. Fix this by adding "cond_resched" to the loop that frees the exceptions.

Reported-by: John Pittman jpittman@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Mikulas Patocka mpatocka@redhat.com Signed-off-by: Mike Snitzer snitzer@kernel.org --- drivers/md/dm-snap.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index bf7a574499a34..0ace06d1bee38 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -684,8 +684,10 @@ static void dm_exception_table_exit(struct dm_exception_table *et, for (i = 0; i < size; i++) { slot = et->table + i;

- hlist_bl_for_each_entry_safe(ex, pos, n, slot, hash_list) + hlist_bl_for_each_entry_safe(ex, pos, n, slot, hash_list) { kmem_cache_free(mem, ex); + cond_resched(); + } }

kvfree(et->table);