Commit 13017b42 authored by Yang Erkun's avatar Yang Erkun Committed by Yu Kuai
Browse files

md: make rdev_addable usable for rcu mode 



Our testcase trigger panic:

BUG: kernel NULL pointer dereference, address: 00000000000000e0
...
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 2 UID: 0 PID: 85 Comm: kworker/2:1 Not tainted 6.16.0+ #94
PREEMPT(none)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.16.1-2.fc37 04/01/2014
Workqueue: md_misc md_start_sync
RIP: 0010:rdev_addable+0x4d/0xf0
...
Call Trace:
 <TASK>
 md_start_sync+0x329/0x480
 process_one_work+0x226/0x6d0
 worker_thread+0x19e/0x340
 kthread+0x10f/0x250
 ret_from_fork+0x14d/0x180
 ret_from_fork_asm+0x1a/0x30
 </TASK>
Modules linked in: raid10
CR2: 00000000000000e0
---[ end trace 0000000000000000 ]---
RIP: 0010:rdev_addable+0x4d/0xf0

md_spares_need_change in md_start_sync will call rdev_addable which
protected by rcu_read_lock/rcu_read_unlock. This rcu context will help
protect rdev won't be released, but rdev->mddev will be set to NULL
before we call synchronize_rcu in md_kick_rdev_from_array. Fix this by
using READ_ONCE and check does rdev->mddev still alive.

Fixes: bc08041b ("md: suspend array in md_start_sync() if array need reconfiguration")
Fixes: 570b9147 ("md: use RCU lock to protect traversal in md_spares_need_change()")
Signed-off-by: default avatarYang Erkun <yangerkun@huawei.com>
Link: https://lore.kernel.org/linux-raid/20250731114530.776670-1-yangerkun@huawei.com


Signed-off-by: default avatarYu Kuai <yukuai3@huawei.com>
parent 178d1391

drivers/md/md.c

+7 −1
Original line number Diff line number Diff line
@@ -9427,6 +9427,12 @@ static bool rdev_is_spare(struct md_rdev *rdev) 


static bool rdev_addable(struct md_rdev *rdev)

{

	struct mddev *mddev;



	mddev = READ_ONCE(rdev->mddev);

	if (!mddev)

		return false;



	/* rdev is already used, don't add it again. */

	if (test_bit(Candidate, &rdev->flags) || rdev->raid_disk >= 0 ||

	    test_bit(Faulty, &rdev->flags))
@@ -9437,7 +9443,7 @@ static bool rdev_addable(struct md_rdev *rdev) 
		return true;



	/* Allow to add if array is read-write. */

	if (md_is_rdwr(rdev->mddev))

	if (md_is_rdwr(mddev))

		return true;



	/*