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: bc08041b32ab ("md: suspend array in md_start_sync() if array need reconfiguration")
Fixes: 570b9147deb6 ("md: use RCU lock to protect traversal in md_spares_need_change()")
Signed-off-by: Yang Erkun <yangerkun@xxxxxxxxxx>
---
drivers/md/md.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 046fe85c76fe..adc5f0b48a00 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -9421,6 +9421,12 @@ 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))
@@ -9431,7 +9437,7 @@ 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;
/*
--
2.39.2
