Re: [syzbot] [kernel?] KCSAN: data-race in kick_pool / wq_worker_running

[Hillf Danton <hdanton@sina.com>]

On Fri, 29 Nov 2024 06:38:26 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    7af08b57bcb9 Merge tag 'trace-v6.13-2' of git://git.kernel..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10a39f5f980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=77174711582263a3
> dashboard link: https://syzkaller.appspot.com/bug?extid=f8761b2f358f6a1dec5e
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/13ed5c4111d5/disk-7af08b57.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b14531c093bd/vmlinux-7af08b57.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/0ddfac565b6b/bzImage-7af08b57.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+f8761b2f358f6a1dec5e@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KCSAN: data-race in kick_pool / wq_worker_running
> 
> read-write to 0xffff888237d2e8a4 of 4 bytes by task 3377 on cpu 1:
>  wq_worker_running+0x98/0x130 kernel/workqueue.c:1400
>  schedule_timeout+0xb8/0x160 kernel/time/sleep_timeout.c:99
>  do_wait_for_common kernel/sched/completion.c:95 [inline]
>  __wait_for_common kernel/sched/completion.c:116 [inline]
>  wait_for_common+0xfb/0x1c0 kernel/sched/completion.c:127
>  usb_start_wait_urb+0xdc/0x190 drivers/usb/core/message.c:64
>  usb_internal_control_msg drivers/usb/core/message.c:103 [inline]
>  usb_control_msg+0x182/0x240 drivers/usb/core/message.c:154
>  get_port_status drivers/usb/core/hub.c:604 [inline]
>  hub_ext_port_status+0xbf/0x480 drivers/usb/core/hub.c:621
>  usb_hub_port_status drivers/usb/core/hub.c:671 [inline]
>  port_event drivers/usb/core/hub.c:5714 [inline]
>  hub_event+0x538/0x2910 drivers/usb/core/hub.c:5903
>  process_one_work kernel/workqueue.c:3229 [inline]
>  process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3310
>  worker_thread+0x51d/0x6f0 kernel/workqueue.c:3391
>  kthread+0x1d1/0x210 kernel/kthread.c:389
>  ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> read to 0xffff888237d2e8a4 of 4 bytes by task 3399 on cpu 0:
>  need_more_worker kernel/workqueue.c:934 [inline]

/*
 * Need to wake up a worker?  Called from anything but currently
 * running workers.
 *
 * Note that, because unbound workers never contribute to nr_running, this
 * function will always return %true for unbound pools as long as the
 * worklist isn't empty.
 */
static bool need_more_worker(struct worker_pool *pool)
{
	return !list_empty(&pool->worklist) && !pool->nr_running;
}

Given bound workers only considered wrt nr_running, this report can be 
safely dropped/ignored as data race is ruled out for them.

>  kick_pool+0x4d/0x2c0 kernel/workqueue.c:1240
>  __queue_work+0x8bb/0xb40 kernel/workqueue.c:2340
>  queue_work_on+0xd3/0x180 kernel/workqueue.c:2390
>  wg_queue_enqueue_per_peer_tx+0x124/0x260 drivers/net/wireguard/queueing.h:188
>  wg_packet_encrypt_worker+0xa00/0xbb0 drivers/net/wireguard/send.c:305
>  process_one_work kernel/workqueue.c:3229 [inline]
>  process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3310
>  worker_thread+0x51d/0x6f0 kernel/workqueue.c:3391
>  kthread+0x1d1/0x210 kernel/kthread.c:389
>  ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> value changed: 0x00000000 -> 0x00000001
> 
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 UID: 0 PID: 3399 Comm: kworker/0:4 Not tainted 6.12.0-syzkaller-10689-g7af08b57bcb9 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> Workqueue: wg-crypt-wg1 wg_packet_encrypt_worker
> ==================================================================
> 
> 
> ---
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