[syzbot] [io-uring?] BUG: corrupted list in io_poll_remove_entries

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e7aa57247700 Merge tag 'spi-fix-v6.19-rc8' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14d3b65a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
dashboard link: https://syzkaller.appspot.com/bug?extid=ab12f0c08dd7ab8d057c
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1222965a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=140e833a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c46beb4ff3a5/disk-e7aa5724.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d162bcaaf9b9/vmlinux-e7aa5724.xz
kernel image: https://storage.googleapis.com/syzbot-assets/54b0844b8ea7/bzImage-e7aa5724.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ab12f0...@syzkaller.appspotmail.com

list_del corruption. prev->next should be ffff88807dc6c3f0, but was ffff888146b205c8. (prev=ffff888146b205c8)
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:62!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5969 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:__list_del_entry_valid_or_report+0x14a/0x1d0 lib/list_debug.c:62
Code: 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 8d 00 00 00 48 8b 55 00 48 89 e9 48 89 de 48 c7 c7 40 3d fa 8b e8 37 b0 32 fc 90 <0f> 0b 4c 89 e7 e8 3c 24 5d fd 48 89 ea 48 b8 00 00 00 00 00 fc ff
RSP: 0018:ffffc90003bffaa8 EFLAGS: 00010082
RAX: 000000000000006d RBX: ffff88807dc6c3f0 RCX: 0000000000000000
RDX: 000000000000006d RSI: ffffffff81e5d6c9 RDI: fffff5200077ff46
RBP: ffff888146b205c8 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000080000001 R11: 0000000000000000 R12: ffff88807dc6c2b0
R13: ffff88807dc6c408 R14: ffff88807dc6c3f0 R15: ffff88807dc6c3c8
FS: 0000000000000000(0000) GS:ffff8881245d9000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f60e56708c0 CR3: 000000006b065000 CR4: 00000000003526f0
Call Trace:
<TASK>
__list_del_entry_valid include/linux/list.h:132 [inline]
__list_del_entry include/linux/list.h:223 [inline]
list_del_init include/linux/list.h:295 [inline]
io_poll_remove_waitq io_uring/poll.c:149 [inline]
io_poll_remove_entry io_uring/poll.c:166 [inline]
io_poll_remove_entries.part.0+0x156/0x7e0 io_uring/poll.c:197
io_poll_remove_entries io_uring/poll.c:177 [inline]
io_poll_task_func+0x39e/0xe30 io_uring/poll.c:343
io_handle_tw_list+0x194/0x580 io_uring/io_uring.c:1122
tctx_task_work_run+0x57/0x2b0 io_uring/io_uring.c:1182
tctx_task_work+0x7a/0xd0 io_uring/io_uring.c:1200
task_work_run+0x150/0x240 kernel/task_work.c:233
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x829/0x2a30 kernel/exit.c:971
do_group_exit+0xd5/0x2a0 kernel/exit.c:1112
__do_sys_exit_group kernel/exit.c:1123 [inline]
__se_sys_exit_group kernel/exit.c:1121 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1121
x64_sys_call+0x14fd/0x1510 arch/x86/include/generated/asm/syscalls_64.h:232
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f60e579aeb9
Code: Unable to access opcode bytes at 0x7f60e579ae8f.
RSP: 002b:00007ffc2d47ddf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f60e579aeb9
RDX: 0000000000000064 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000003 R08: 0000000000000000 R09: 00007f60e59e1280
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f60e59e1280 R14: 0000000000000003 R15: 00007ffc2d47deb0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__list_del_entry_valid_or_report+0x14a/0x1d0 lib/list_debug.c:62
Code: 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 8d 00 00 00 48 8b 55 00 48 89 e9 48 89 de 48 c7 c7 40 3d fa 8b e8 37 b0 32 fc 90 <0f> 0b 4c 89 e7 e8 3c 24 5d fd 48 89 ea 48 b8 00 00 00 00 00 fc ff
RSP: 0018:ffffc90003bffaa8 EFLAGS: 00010082
RAX: 000000000000006d RBX: ffff88807dc6c3f0 RCX: 0000000000000000
RDX: 000000000000006d RSI: ffffffff81e5d6c9 RDI: fffff5200077ff46
RBP: ffff888146b205c8 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000080000001 R11: 0000000000000000 R12: ffff88807dc6c2b0
R13: ffff88807dc6c408 R14: ffff88807dc6c3f0 R15: ffff88807dc6c3c8
FS: 0000000000000000(0000) GS:ffff8881245d9000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f60e56708c0 CR3: 000000006b065000 CR4: 00000000003526f0


---
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[Jens Axboe]

This looks like a bug related to dvb polling, presumably in dvb_dvr_poll()
or friends. I've seen that in drivers before, for example comedi, see:

commit 35b6fc51c666fc96355be5cd633ed0fe4ccf68b2
Author: Ian Abbott <abb...@mev.co.uk>
Date: Tue Jul 22 16:53:16 2025 +0100

comedi: fix race between polling and detaching

as a reference.

#syz set subsystems: media

--
Jens Axboe

[Jens Axboe]

On 2/9/26 11:26 AM, syzbot wrote:

#syz test

diff --git a/drivers/media/dvb-core/dmxdev.c b/drivers/media/dvb-core/dmxdev.c
index 8c6f5aafda1d..5cb46109d1ff 100644
--- a/drivers/media/dvb-core/dmxdev.c
+++ b/drivers/media/dvb-core/dmxdev.c
@@ -168,7 +168,9 @@ static int dvb_dvr_open(struct inode *inode, struct file *file)
mutex_unlock(&dmxdev->mutex);
return -ENOMEM;
}
- dvb_ringbuffer_init(&dmxdev->dvr_buffer, mem, DVR_BUFFER_SIZE);
+ dmxdev->dvr_buffer.data = mem;
+ dmxdev->dvr_buffer.size = DVR_BUFFER_SIZE;
+ dvb_ringbuffer_reset(&dmxdev->dvr_buffer);
if (dmxdev->may_do_mmap)
dvb_vb2_init(&dmxdev->dvr_vb2_ctx, "dvr",
file->f_flags & O_NONBLOCK);

--
Jens Axboe

[syzbot]

Hello,

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

Reported-by: syzbot+ab12f0...@syzkaller.appspotmail.com
Tested-by: syzbot+ab12f0...@syzkaller.appspotmail.com

Tested on:

commit: 05f7e89a Linux 6.19
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15956a52580000

kernel config: https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
dashboard link: https://syzkaller.appspot.com/bug?extid=ab12f0c08dd7ab8d057c
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

patch: https://syzkaller.appspot.com/x/patch.diff?x=17da94aa580000

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

[Jens Axboe]

As per the other email, I believe this analysis was correct. Here's an
epoll based reproducer for the same issue, showing the problem with dvb
blowing away poll waitqueues. Crash here:

list_del corruption. prev->next should be ff1100004a299148, but was ff1100004169c5c8. (prev=ff1100004169c5c8)

------------[ cut here ]------------
kernel BUG at lib/list_debug.c:62!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI

CPU: 0 UID: 0 PID: 10044 Comm: dvr-poll-repro Not tainted 6.19.0-g05f7e89ab973 #422 PREEMPT(full)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:__list_del_entry_valid_or_report+0x178/0x280
Code: fc ff df 48 89 d1 48 c1 e9 03 80 3c 01 00 0f 85 07 01 00 00 48 8b 02 48 89 d1 48 c7 c7 40 44 1a 8c 48 89 c2 e8 39 d5 2e fc 90 <0f> 0b 48 89 cf 48 89 74 24 10 48 89 0c 24 48 89 44 24 08 e8 b0 2b
RSP: 0018:ffa000000c74fd30 EFLAGS: 00010082
RAX: 000000000000006d RBX: ff1100004a299130 RCX: 0000000000000000
RDX: 000000000000006d RSI: ffffffff81e76a0e RDI: fff3fc00018e9f97
RBP: ff1100004a299148 R08: ffffffff81e6f6f7 R09: 0000000000000001
R10: 0000000000000005 R11: 0000000000000000 R12: ff1100004169c588
R13: 0000000000000286 R14: ff1100004a354c00 R15: ff1100004a299120
FS: 00007f486cac8740(0000) GS:ff110000975d4000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00005599332e7fe0 CR3: 000000006a752000 CR4: 0000000000351ef0
Call Trace:
<TASK>
? srso_alias_return_thunk+0x5/0xfbef5
remove_wait_queue+0x28/0x1b0
ep_remove_wait_queue+0x85/0x1d0
ep_clear_and_put+0x186/0x420
? __pfx_ep_eventpoll_release+0x10/0x10
ep_eventpoll_release+0x3e/0x60
__fput+0x3fd/0xb40
fput_close_sync+0x113/0x250
? __pfx_fput_close_sync+0x10/0x10
__x64_sys_close+0x8b/0x120
do_syscall_64+0xcb/0xf80
? srso_alias_return_thunk+0x5/0xfbef5
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f486cb5ceb2
Code: 18 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 75 1a 83 e2 39 83 fa 08 75 12 e8 2b ff ff ff 0f 1f 00 49 89 ca 48 8b 44 24 20 0f 05 <48> 83 c4 18 c3 66 0f 1f 84 00 00 00 00 00 48 83 ec 10 ff 74 24 18
RSP: 002b:00007ffe5521f0b0 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f486cb5ceb2
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007ffe5521f140 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000001
R13: 00007f486cd0a000 R14: 00007ffe5521f298 R15: 00005643adab8dd8

</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---

RIP: 0010:__list_del_entry_valid_or_report+0x178/0x280
Code: fc ff df 48 89 d1 48 c1 e9 03 80 3c 01 00 0f 85 07 01 00 00 48 8b 02 48 89 d1 48 c7 c7 40 44 1a 8c 48 89 c2 e8 39 d5 2e fc 90 <0f> 0b 48 89 cf 48 89 74 24 10 48 89 0c 24 48 89 44 24 08 e8 b0 2b
RSP: 0018:ffa000000c74fd30 EFLAGS: 00010082
RAX: 000000000000006d RBX: ff1100004a299130 RCX: 0000000000000000
RDX: 000000000000006d RSI: ffffffff81e76a0e RDI: fff3fc00018e9f97
RBP: ff1100004a299148 R08: ffffffff81e6f6f7 R09: 0000000000000001
R10: 0000000000000005 R11: 0000000000000000 R12: ff1100004169c588
R13: 0000000000000286 R14: ff1100004a354c00 R15: ff1100004a299120
FS: 00007f486cac8740(0000) GS:ff110000975d4000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00005599332e7fe0 CR3: 000000006a752000 CR4: 0000000000351ef0

Reproducer:


#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/epoll.h>
#include <unistd.h>

#define DVR_PATH "/dev/dvb/adapter0/dvr0"
#define NR_ITERATIONS 100

static int test_dvr_poll(int iter)
{
struct epoll_event ev;
int dvr_fd, dvr_fd2, epfd;
int ret = -1;

dvr_fd = open(DVR_PATH, O_RDWR | O_WRONLY);
if (dvr_fd < 0) {
perror("open " DVR_PATH);
return -1;
}

epfd = epoll_create1(0);
if (epfd < 0) {
perror("epoll_create1");
goto close_dvr;
}
memset(&ev, 0, sizeof(ev));
ev.events = EPOLLIN;
ev.data.fd = dvr_fd;
if (epoll_ctl(epfd, EPOLL_CTL_ADD, dvr_fd, &ev) < 0) {
perror("epoll_ctl ADD");
goto close_ep;
}

dvr_fd2 = open(DVR_PATH, O_RDONLY);
if (dvr_fd2 < 0) {
perror("open " DVR_PATH " O_RDONLY");
goto close_ep;
}

close(dvr_fd2);
ret = 0;
close_ep:
close(epfd);
close_dvr:
close(dvr_fd);
return ret;
}

int main(int argc, char *argv[])
{
int i, iterations = NR_ITERATIONS;

if (argc > 1)
iterations = atoi(argv[1]);

for (i = 0; i < iterations; i++) {
if (test_dvr_poll(i))
return 1;
}

return 0;
}

--
Jens Axboe