linux-kernel - [PATCH -next v3] md/raid5-cache: fix a deadlock in r5l_exit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20230708091727.1417894-1-yukuai1@huaweicloud.com>
Date:   Sat,  8 Jul 2023 17:17:27 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     song@...nel.org, logang@...tatee.com, axboe@...nel.dk
Cc:     linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        yukuai3@...wei.com, yukuai1@...weicloud.com, yi.zhang@...wei.com,
        yangerkun@...wei.com
Subject: [PATCH -next v3] md/raid5-cache: fix a deadlock in r5l_exit_log()

From: Yu Kuai <yukuai3@...wei.com>

Commit b13015af94cf ("md/raid5-cache: Clear conf->log after finishing
work") introduce a new problem:

// caller hold reconfig_mutex
r5l_exit_log
 flush_work(&log->disable_writeback_work)
			r5c_disable_writeback_async
			 wait_event
			  /*
			   * conf->log is not NULL, and mddev_trylock()
			   * will fail, wait_event() can never pass.
			   */
 conf->log = NULL

Fix this problem by setting 'config->log' to NULL before wake_up() as it
used to be, so that wait_event() from r5c_disable_writeback_async() can
exist. In the meantime, move forward md_unregister_thread() so that
null-ptr-deref this commit fixed can still be fixed.

Fixes: b13015af94cf ("md/raid5-cache: Clear conf->log after finishing work")
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---

Changes in v3:
 - Use a different solution.

 drivers/md/raid5-cache.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 47ba7d9e81e1..2eac4a50d99b 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -3168,12 +3168,15 @@ void r5l_exit_log(struct r5conf *conf)
 {
 	struct r5l_log *log = conf->log;
 
-	/* 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);
 
+	/*
+	 * 'reconfig_mutex' is held by caller, set 'confg->log' to NULL to
+	 * ensure disable_writeback_work wakes up and exits.
+	 */
 	conf->log = NULL;
+	wake_up(&conf->mddev->sb_wait);
+	flush_work(&log->disable_writeback_work);
 
 	mempool_exit(&log->meta_pool);
 	bioset_exit(&log->bs);
-- 
2.39.2