[syzbot] [block?] BUG: corrupted list in loop_process_work

Hello,

syzbot found the following issue on:

HEAD commit: c674aa7c289e Add linux-next specific files for 20250212
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=125063f8580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a0fd539126ae5541
dashboard link: https://syzkaller.appspot.com/bug?extid=c104904eeb2c0edbdb06
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=158a3bdf980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17e18aa4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cc5b357d26d3/disk-c674aa7c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/11dcf272a27b/vmlinux-c674aa7c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4e487b1c1c6e/bzImage-c674aa7c.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/4ea41e9eae4d/mount_0.gz

The issue was bisected to:

commit 3bee991f2b68175c828dc3f9c26367fe1827319a
Author: Zhaoyang Huang <[email protected]>
Date: Fri Feb 7 09:19:42 2025 +0000

loop: release the lo_work_lock before queue_work

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=161029b0580000
final oops: https://syzkaller.appspot.com/x/report.txt?x=151029b0580000
console output: https://syzkaller.appspot.com/x/log.txt?x=111029b0580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]
Fixes: 3bee991f2b68 ("loop: release the lo_work_lock before queue_work")

list_add double add: new=ffff88807fe21c70, prev=ffff88807fe21c70, next=ffff888024c29160.
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:37!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 1 UID: 0 PID: 12 Comm: kworker/u8:1 Not tainted 6.14.0-rc2-next-20250212-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Workqueue: loop0 loop_workfn
RIP: 0010:__list_add_valid_or_report+0xa4/0x130 lib/list_debug.c:35
Code: f7 74 11 b0 01 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc 48 c7 c7 40 e5 60 8c 4c 89 fe 4c 89 e2 4c 89 f1 e8 fd 88 35 fc 90 <0f> 0b 48 c7 c7 40 e3 60 8c e8 ee 88 35 fc 90 0f 0b 48 c7 c7 e0 e3
RSP: 0018:ffffc90000117628 EFLAGS: 00010046
RAX: 0000000000000058 RBX: 1ffff1100ffc438e RCX: 89e05f8d6ffcb000
RDX: 0000000000000000 RSI: 0000000080000001 RDI: 0000000000000000
RBP: 1ffff1100498522d R08: ffffffff819f562c R09: 1ffff92000022e60
R10: dffffc0000000000 R11: fffff52000022e61 R12: ffff88807fe21c70
R13: dffffc0000000000 R14: ffff888024c29160 R15: ffff88807fe21c70
FS: 0000000000000000(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff4b64ffe00 CR3: 000000007cfa4000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__list_add_valid include/linux/list.h:88 [inline]
__list_add include/linux/list.h:150 [inline]
list_add_tail include/linux/list.h:183 [inline]
loop_process_work+0x1f96/0x21c0 drivers/block/loop.c:1977
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3317
worker_thread+0x870/0xd30 kernel/workqueue.c:3398
kthread+0x7a9/0x920 kernel/kthread.c:464
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__list_add_valid_or_report+0xa4/0x130 lib/list_debug.c:35
Code: f7 74 11 b0 01 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc 48 c7 c7 40 e5 60 8c 4c 89 fe 4c 89 e2 4c 89 f1 e8 fd 88 35 fc 90 <0f> 0b 48 c7 c7 40 e3 60 8c e8 ee 88 35 fc 90 0f 0b 48 c7 c7 e0 e3
RSP: 0018:ffffc90000117628 EFLAGS: 00010046
RAX: 0000000000000058 RBX: 1ffff1100ffc438e RCX: 89e05f8d6ffcb000
RDX: 0000000000000000 RSI: 0000000080000001 RDI: 0000000000000000
RBP: 1ffff1100498522d R08: ffffffff819f562c R09: 1ffff92000022e60
R10: dffffc0000000000 R11: fffff52000022e61 R12: ffff88807fe21c70
R13: dffffc0000000000 R14: ffff888024c29160 R15: ffff88807fe21c70
FS: 0000000000000000(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff4b64ffe00 CR3: 000000007cfa4000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
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On Fri, 14 Feb 2025 11:58:24 -0800
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17e18aa4580000

#syz test

--- x/drivers/block/loop.c
+++ y/drivers/block/loop.c
@@ -1974,7 +1974,8 @@ static void loop_process_work(struct loo
*/
if (worker && !work_pending(&worker->work)) {
worker->last_ran_at = jiffies;
- list_add_tail(&worker->idle_list, &lo->idle_worker_list);
+ if (list_empty(&worker->idle_list))
+ list_add_tail(&worker->idle_list, &lo->idle_worker_list);
loop_set_timer(lo);
}
spin_unlock_irq(&lo->lo_work_lock);
--

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: [email protected]
Tested-by: [email protected]

Tested on:

commit: 0ae0fa3b Add linux-next specific files for 20250214
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13a5d9a4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c67242141a7e5bdd
patch: https://syzkaller.appspot.com/x/patch.diff?x=12220898580000

Note: testing is done by a robot and is best-effort only.

#syz test

Hello Zhaoyang,
> #syz test
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 68c943a77e41..354d77f9228b 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1972,7 +1972,8 @@ static void loop_process_work(struct loop_worker *worker,
> * *and* the worker will not run again which ensures that it
> * is safe to free any worker on the idle list
> */
> - if (worker && !work_pending(&worker->work)) {
> + if (worker && !work_pending(&worker->work)
> + && list_empty(&worker->idle_list)) {
> worker->last_ran_at = jiffies;
The `work` to be queued may originate from RB tree or lo->rootcg_work, so it may
be freed during queuing without the lock.

I think you may need to revert the patch.


Thanks,
Ming