dm snapshot: fix lockup in dm_exception_table_exit

stable inclusion
from stable-v5.4.274
commit e7d4cff57c3c43fdd72342c78d4138f509c7416e
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9Q9CC
CVE: CVE-2024-35805

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7d4cff57c3c43fdd72342c78d4138f509c7416e



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[ Upstream commit 6e7132ed3c07bd8a6ce3db4bb307ef2852b322dc ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Conflicts:
  drivers/md/dm-snap.c
[Commit f79ae415 change the way to traverse exception]
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>