[syzbot] WARNING in kernfs_remove_by_name_ns (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d07f6ca9 Linux 5.13-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13313bc7d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=dddb87edd6431081
dashboard link: https://syzkaller.appspot.com/bug?extid=415759e3b545070f5de3

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+415759...@syzkaller.appspotmail.com

------------[ cut here ]------------
kernfs: can not remove 'nr_tags', no directory
WARNING: CPU: 0 PID: 13503 at fs/kernfs/dir.c:1508 kernfs_remove_by_name_ns+0x98/0xb0 fs/kernfs/dir.c:1508
Modules linked in:
CPU: 0 PID: 13503 Comm: syz-executor.5 Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:kernfs_remove_by_name_ns+0x98/0xb0 fs/kernfs/dir.c:1508
Code: 84 ff 48 c7 c7 80 49 14 8c 41 bc fe ff ff ff e8 2e 2b 27 07 eb d9 e8 47 37 84 ff 4c 89 e6 48 c7 c7 60 97 7c 89 e8 9b 33 e4 06 <0f> 0b 41 bc fe ff ff ff eb bb 66 66 2e 0f 1f 84 00 00 00 00 00 0f
RSP: 0018:ffffc90009d4fa38 EFLAGS: 00010286
RAX: 0000000000000000 RBX: ffffffff8c7ddb08 RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff815cda35 RDI: fffff520013a9f39
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff815c789e R11: 0000000000000000 R12: ffffffff89c12040
R13: 0000000000000000 R14: ffffffff89c11f60 R15: dffffc0000000000
FS: 00007f736e995700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd8b06a9030 CR3: 00000000282c4000 CR4: 0000000000350ef0
Call Trace:
kernfs_remove_by_name include/linux/kernfs.h:593 [inline]
remove_files+0x96/0x1c0 fs/sysfs/group.c:28
sysfs_remove_group+0x87/0x170 fs/sysfs/group.c:289
sysfs_remove_groups fs/sysfs/group.c:313 [inline]
sysfs_remove_groups+0x5c/0xa0 fs/sysfs/group.c:305
__kobject_del+0x89/0x200 lib/kobject.c:611
kobject_del lib/kobject.c:643 [inline]
kobject_del+0x3c/0x60 lib/kobject.c:635
blk_mq_unregister_hctx block/blk-mq-sysfs.c:238 [inline]
blk_mq_unregister_hctx block/blk-mq-sysfs.c:227 [inline]
blk_mq_sysfs_unregister+0x227/0x300 block/blk-mq-sysfs.c:357
__blk_mq_update_nr_hw_queues block/blk-mq.c:3685 [inline]
blk_mq_update_nr_hw_queues+0x48f/0xd30 block/blk-mq.c:3725
nbd_start_device+0x1e3/0xd50 drivers/block/nbd.c:1270
nbd_start_device_ioctl drivers/block/nbd.c:1320 [inline]
__nbd_ioctl drivers/block/nbd.c:1392 [inline]
nbd_ioctl+0x527/0xa50 drivers/block/nbd.c:1432
blkdev_ioctl+0x2a1/0x6d0 block/ioctl.c:585
block_ioctl+0xf9/0x140 fs/block_dev.c:1664
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:1069 [inline]
__se_sys_ioctl fs/ioctl.c:1055 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4665d9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f736e995188 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 00000000004665d9
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000007
RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60
R13: 00007ffe01d6a66f R14: 00007f736e995300 R15: 0000000000022000


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[Hillf Danton]

On Fri, 21 May 2021 00:08:24 -0700

Add rollback in case of error on registering hctx, with no idea if it
helps fix the problem reported by syzbot.

+++ x/block/blk-mq-sysfs.c
@@ -242,7 +242,7 @@ static int blk_mq_register_hctx(struct b
{
struct request_queue *q = hctx->queue;
struct blk_mq_ctx *ctx;
- int i, ret;
+ int i, j, ret;

if (!hctx->nr_ctx)
return 0;
@@ -254,9 +254,17 @@ static int blk_mq_register_hctx(struct b
hctx_for_each_ctx(hctx, ctx, i) {
ret = kobject_add(&ctx->kobj, &hctx->kobj, "cpu%u", ctx->cpu);
if (ret)
- break;
+ goto rollback;
}
+ return 0;

+rollback:
+ hctx_for_each_ctx(hctx, ctx, j) {
+ if (j == i)
+ break;
+ kobject_del(&ctx->kobj);
+ }
+ kobject_del(&hctx->kobj);
return ret;
}

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.