Skip to content

Commit ed3b98c

Browse files
shligitshligit
committed
MD: add rdev reference for super write
Xiao Ni reported below crash: [26396.335146] BUG: unable to handle kernel NULL pointer dereference at 00000000000002a8 [26396.342990] IP: [<ffffffffa0425b00>] super_written+0x20/0x80 [md_mod] [26396.349449] PGD 0 [26396.351468] Oops: 0002 [#1] SMP [26396.354898] Modules linked in: ext4 mbcache jbd2 raid456 async_raid6_recov async_memcpy async_pq async_xor xor async_td [26396.408404] CPU: 5 PID: 3261 Comm: loop0 Not tainted 4.5.0 #1 [26396.414140] Hardware name: Dell Inc. PowerEdge R715/0G2DP3, BIOS 3.2.2 09/15/2014 [26396.421608] task: ffff8808339be680 ti: ffff8808365f4000 task.ti: ffff8808365f4000 [26396.429074] RIP: 0010:[<ffffffffa0425b00>] [<ffffffffa0425b00>] super_written+0x20/0x80 [md_mod] [26396.437952] RSP: 0018:ffff8808365f7c38 EFLAGS: 00010046 [26396.443252] RAX: ffffffffa0425ae0 RBX: ffff8804336a7900 RCX: ffffe8f9f7b41198 [26396.450371] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8804336a7900 [26396.457489] RBP: ffff8808365f7c50 R08: 0000000000000005 R09: 00001801e02ce3d7 [26396.464608] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000 [26396.471728] R13: ffff8808338d9a00 R14: 0000000000000000 R15: ffff880833f9fe00 [26396.478849] FS: 00007f9e5066d740(0000) GS:ffff880237b40000(0000) knlGS:0000000000000000 [26396.486922] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [26396.492656] CR2: 00000000000002a8 CR3: 00000000019ea000 CR4: 00000000000006e0 [26396.499775] Stack: [26396.501781] ffff8804336a7900 0000000000000000 0000000000000000 ffff8808365f7c68 [26396.509199] ffffffff81308cd0 ffff8804336a7900 ffff8808365f7ca8 ffffffff81310637 [26396.516618] 00000000a0233a00 ffff880833f9fe00 0000000000000000 ffff880833fb0000 [26396.524038] Call Trace: [26396.526485] [<ffffffff81308cd0>] bio_endio+0x40/0x60 [26396.531529] [<ffffffff81310637>] blk_update_request+0x87/0x320 [26396.537439] [<ffffffff8131a20a>] blk_mq_end_request+0x1a/0x70 [26396.543261] [<ffffffff81313889>] blk_flush_complete_seq+0xd9/0x2a0 [26396.549517] [<ffffffff81313ccf>] flush_end_io+0x15f/0x240 [26396.554993] [<ffffffff8131a22a>] blk_mq_end_request+0x3a/0x70 [26396.560815] [<ffffffff8131a314>] __blk_mq_complete_request+0xb4/0xe0 [26396.567246] [<ffffffff8131a35c>] blk_mq_complete_request+0x1c/0x20 [26396.573506] [<ffffffffa04182df>] loop_queue_work+0x6f/0x72c [loop] [26396.579764] [<ffffffff81697844>] ? __schedule+0x2b4/0x8f0 [26396.585242] [<ffffffff810a7812>] kthread_worker_fn+0x52/0x170 [26396.591065] [<ffffffff810a77c0>] ? kthread_create_on_node+0x1a0/0x1a0 [26396.597582] [<ffffffff810a7238>] kthread+0xd8/0xf0 [26396.602453] [<ffffffff810a7160>] ? kthread_park+0x60/0x60 [26396.607929] [<ffffffff8169bdcf>] ret_from_fork+0x3f/0x70 [26396.613319] [<ffffffff810a7160>] ? kthread_park+0x60/0x60 md_super_write() and corresponding md_super_wait() generally are called with reconfig_mutex locked, which prevents disk disappears. There is one case this rule is broken. write_sb_page of bitmap.c doesn't hold the mutex. next_active_rdev does increase rdev reference, but it decreases the reference too early (eg, before IO finish). disk can disappear at the window. We unconditionally increase rdev reference in md_super_write() to avoid the race. Reported-and-tested-by: Xiao Ni <xni@redhat.com> Reviewed-by: Neil Brown <neilb@suse.de> Signed-off-by: Shaohua Li <shli@fb.com>
1 parent 466ad29 commit ed3b98c

File tree

1 file changed

+3
-0
lines changed

1 file changed

+3
-0
lines changed

‎drivers/md/md.c

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -718,6 +718,7 @@ static void super_written(struct bio *bio)
718718

719719
if (atomic_dec_and_test(&mddev->pending_writes))
720720
wake_up(&mddev->sb_wait);
721+
rdev_dec_pending(rdev, mddev);
721722
bio_put(bio);
722723
}
723724

@@ -732,6 +733,8 @@ void md_super_write(struct mddev *mddev, struct md_rdev *rdev,
732733
*/
733734
struct bio *bio = bio_alloc_mddev(GFP_NOIO, 1, mddev);
734735

736+
atomic_inc(&rdev->nr_pending);
737+
735738
bio->bi_bdev = rdev->meta_bdev ? rdev->meta_bdev : rdev->bdev;
736739
bio->bi_iter.bi_sector = sector;
737740
bio_add_page(bio, page, size, 0);

0 commit comments

Comments
 (0)