linux-kernel - [PATCH] dm: do not assign error to md->kworker

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Message-Id: <1476753409-16111-1-git-send-email-tahsin@google.com>
Date:   Mon, 17 Oct 2016 18:16:48 -0700
From:   Tahsin Erdogan <tahsin@...gle.com>
To:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Shaohua Li <shli@...nel.org>
Cc:     linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tahsin Erdogan <tahsin@...gle.com>
Subject: [PATCH] dm: do not assign error to md->kworker_task

cleanup_mapped_device() calls kthread_stop() if kworker_task is
non-NULL. Currently the assigned value could be a valid task struct or
an error code. Do not assign in case of error.

Example failure when kthread_run() returns -ENOMEM:

[   22.255939] BUG: unable to handle kernel NULL pointer dereference at 000000000000000c
[   22.258847] IP: [<ffffffff802973a4>] kthread_stop+0x34/0x260
[   22.260130] PGD 78a23067 PUD 78b56067 PMD 0
[   22.260130] Oops: 0002 [#1] SMP
[   22.260130] CPU: 1 PID: 1849 Comm: dmsetup Tainted: G        W 4.8.0+ #3
[   22.260130] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[   22.260130] task: ffff880078966400 task.stack: ffffc90001898000
[   22.260130] RIP: 0010:[<ffffffff802973a4>]  [<ffffffff802973a4>] kthread_stop+0x34/0x260
[   22.260130] RSP: 0018:ffffc9000189bc40  EFLAGS: 00010202
[   22.260130] RAX: 0000000000000001 RBX: fffffffffffffff4 RCX: 0000000000000003
[   22.260130] RDX: ffff88007fd18600 RSI: 0000000000000001 RDI: ffffffff81037080
[   22.260130] RBP: ffffc9000189bc50 R08: 0000000000000000 R09: 0000000000000000
[   22.260130] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
[   22.260130] R13: 0000000000000001 R14: ffff880077f539d8 R15: 0000000000000004
[   22.260130] FS:  00007fc9ef2e2840(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000
[   22.260130] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   22.260130] CR2: 000000000000000c CR3: 0000000077fa2000 CR4: 00000000000006e0
[   22.260130] Stack:
[   22.260130]  ffff880077f53800 0000000000000000 ffffc9000189bc68 ffffffff808b26fa
[   22.260130]  ffff880077f53800 ffffc9000189bcb0 ffffffff808b3c58 0000000000000000
[   22.260130]  00000000808b534b ffffc9000189bd20 ffff880077f53800 0000000000000000
[   22.260130] Call Trace:
[   22.260130]  [<ffffffff808b26fa>] cleanup_mapped_device+0x2a/0xe0
[   22.260130]  [<ffffffff808b3c58>] __dm_destroy+0x1a8/0x2b0
[   22.260130]  [<ffffffff808b4b6e>] dm_destroy+0xe/0x10
[   22.260130]  [<ffffffff808b9f49>] dev_remove+0xd9/0x120
[   22.260130]  [<ffffffff808b9e70>] ? dev_suspend+0x210/0x210
[   22.260130]  [<ffffffff808ba576>] ctl_ioctl+0x206/0x500
[   22.260130]  [<ffffffff808ba87e>] dm_ctl_ioctl+0xe/0x20
[   22.260130]  [<ffffffff803bca40>] do_vfs_ioctl+0x90/0x6b0
[   22.260130]  [<ffffffff80b11fd7>] ?  entry_SYSCALL_64_fastpath+0x5/0xad
[   22.260130]  [<ffffffff802bd974>] ?  trace_hardirqs_on_caller+0xf4/0x1c0
[   22.260130]  [<ffffffff803bd0d4>] SyS_ioctl+0x74/0x80
[   22.260130]  [<ffffffff80b11fea>] entry_SYSCALL_64_fastpath+0x18/0xad
[   22.260130] Code: e5 41 54 85 c0 53 48 89 fb 0f 8f bb 01 00 00 65 8b
05 a1 2d d7 7f 89 c0 48 0f a3 05 9f 94 e8 00 0f 92 c0 84 c0 0f 85 a3 00
00 00 <f0> ff 43 18 48 89 df e8 10 f8 ff ff 48 85 c0 49 89 c4 74 29 f0
[   22.260130] RIP  [<ffffffff802973a4>] kthread_stop+0x34/0x260
[   22.260130]  RSP <ffffc9000189bc40>
[   22.260130] CR2: 000000000000000c
[   22.301062] ---[ end trace 22b4f4f62c04f3cf ]---

Signed-off-by: Tahsin Erdogan <tahsin@...gle.com>
---
 drivers/md/dm-rq.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 5eacce1ef88b..6e5197414a57 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -841,6 +841,8 @@ static void dm_old_request_fn(struct request_queue *q)
  */
 int dm_old_init_request_queue(struct mapped_device *md)
 {
+	struct task_struct *task;
+
 	/* Fully initialize the queue */
 	if (!blk_init_allocated_queue(md->queue, dm_old_request_fn, NULL))
 		return -EINVAL;
@@ -854,11 +856,12 @@ int dm_old_init_request_queue(struct mapped_device *md)
 
 	/* Initialize the request-based DM worker thread */
 	init_kthread_worker(&md->kworker);
-	md->kworker_task = kthread_run(kthread_worker_fn, &md->kworker,
-				       "kdmwork-%s", dm_device_name(md));
-	if (IS_ERR(md->kworker_task))
-		return PTR_ERR(md->kworker_task);
+	task = kthread_run(kthread_worker_fn, &md->kworker, "kdmwork-%s",
+			   dm_device_name(md));
+	if (IS_ERR(task))
+		return PTR_ERR(task);
 
+	md->kworker_task = task;
 	elv_register_queue(md->queue);
 
 	return 0;
-- 
2.8.0.rc3.226.g39d4020