linux-kernel - [RESEND PATCH V5 1/7] ublk_drv: check 'current' instead of 'ubq

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

Message-Id: <20220923061505.52007-2-ZiyangZhang@linux.alibaba.com>
Date:   Fri, 23 Sep 2022 14:14:59 +0800
From:   ZiyangZhang <ZiyangZhang@...ux.alibaba.com>
To:     ming.lei@...hat.com
Cc:     axboe@...nel.dk, xiaoguang.wang@...ux.alibaba.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com,
        ZiyangZhang <ZiyangZhang@...ux.alibaba.com>
Subject: [RESEND PATCH V5 1/7] ublk_drv: check 'current' instead of 'ubq_daemon'

This check is not atomic. So with recovery feature, ubq_daemon may be
modified simultaneously by recovery task. Instead, check 'current' is
safe here because 'current' never changes.

Also add comment explaining this check, which is really important for
understanding recovery feature.

Signed-off-by: ZiyangZhang <ZiyangZhang@...ux.alibaba.com>
Reviewed-by: Ming Lei <ming.lei@...hat.com>
---
 drivers/block/ublk_drv.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 6a4a94b4cdf4..c39b67d7133d 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -645,14 +645,22 @@ static inline void __ublk_rq_task_work(struct request *req)
 	struct ublk_device *ub = ubq->dev;
 	int tag = req->tag;
 	struct ublk_io *io = &ubq->ios[tag];
-	bool task_exiting = current != ubq->ubq_daemon || ubq_daemon_is_dying(ubq);
 	unsigned int mapped_bytes;
 
 	pr_devel("%s: complete: op %d, qid %d tag %d io_flags %x addr %llx\n",
 			__func__, io->cmd->cmd_op, ubq->q_id, req->tag, io->flags,
 			ublk_get_iod(ubq, req->tag)->addr);
 
-	if (unlikely(task_exiting)) {
+	/*
+	 * Task is exiting if either:
+	 *
+	 * (1) current != ubq_daemon.
+	 * io_uring_cmd_complete_in_task() tries to run task_work
+	 * in a workqueue if ubq_daemon(cmd's task) is PF_EXITING.
+	 *
+	 * (2) current->flags & PF_EXITING.
+	 */
+	if (unlikely(current != ubq->ubq_daemon || current->flags & PF_EXITING)) {
 		blk_mq_end_request(req, BLK_STS_IOERR);
 		mod_delayed_work(system_wq, &ub->monitor_work, 0);
 		return;
-- 
2.27.0