> Hello.
>
> syzbot is still reporting warning in kcov_remote_start() from
> __usb_hcd_giveback_urb() path. I guess that commit 8fea0c8fda30
> ("usb: core: hcd: Convert from tasklet to BH workqueue") broke
> the in_serving_softirq() workaround explained in commit e89eed02a5f1
> ("kcov, usb: hide in_serving_softirq checks in __usb_hcd_giveback_urb").
>
> How can we fix this workaround?
>
>
> -----------[ cut here ]------------
> WARNING: CPU: 0 PID: 16 at kernel/kcov.c:870 kcov_remote_start+0x5a2/0x7e0 kernel/kcov.c:870
> Modules linked in:
> CPU: 0 PID: 16 Comm: ksoftirqd/0 Not tainted 6.9.0-rc7-next-20240510-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
> RIP: 0010:kcov_remote_start+0x5a2/0x7e0 kernel/kcov.c:870
> Code: 24 00 00 00 00 9c 8f 04 24 f7 04 24 00 02 00 00 0f 85 a6 01 00 00 41 f7 c6 00 02 00 00 0f 84 93 fa ff ff fb e9 8d fa ff ff 90 <0f> 0b 90 e8 26 71 f4 09 89 c0 48 c7 c7 c8 d4 02 00 48 03 3c c5 e0
> RSP: 0018:ffffc900000079c0 EFLAGS: 00010002
> RAX: 0000000080010101 RBX: ffff8880172cda00 RCX: 0000000000000002
> RDX: dffffc0000000000 RSI: ffffffff8bcac680 RDI: ffffffff8c1fdcc0
> RBP: 0100000000000004 R08: ffffffff92fb25f7 R09: 1ffffffff25f64be
> R10: dffffc0000000000 R11: fffffbfff25f64bf R12: ffffffff8196262e
> R13: 00000000ffffffb9 R14: 0000000000000006 R15: ffff8880b942d4c8
> FS: 0000000000000000(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f3793bff800 CR3: 000000001eccc000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <IRQ>
> kcov_remote_start_usb include/linux/kcov.h:53 [inline]
> kcov_remote_start_usb_softirq include/linux/kcov.h:66 [inline]
> __usb_hcd_giveback_urb+0x34a/0x530 drivers/usb/core/hcd.c:1647
> dummy_timer+0x830/0x45d0 drivers/usb/gadget/udc/dummy_hcd.c:1987
> __run_hrtimer kernel/time/hrtimer.c:1687 [inline]
> __hrtimer_run_queues+0x5a5/0xd50 kernel/time/hrtimer.c:1751
> hrtimer_interrupt+0x396/0x990 kernel/time/hrtimer.c:1813
> local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1032 [inline]
> __sysvec_apic_timer_interrupt+0x110/0x3f0 arch/x86/kernel/apic/apic.c:1049
> instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
> sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1043
> </IRQ>
> <TASK>
> asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
> RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
> RIP: 0010:_raw_spin_unlock_irqrestore+0xd8/0x140 kernel/locking/spinlock.c:194
> Code: 9c 8f 44 24 20 42 80 3c 23 00 74 08 4c 89 f7 e8 6e 7a 66 f6 f6 44 24 21 02 75 52 41 f7 c7 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> c3 3a d0 f5 65 8b 05 34 7a 6e 74 85 c0 74 43 48 c7 04 24 0e 36
> RSP: 0018:ffffc900001577c0 EFLAGS: 00000206
> RAX: 51fa7c47925ba500 RBX: 1ffff9200002aefc RCX: ffffffff8172dd7a
> RDX: dffffc0000000000 RSI: ffffffff8bcab500 RDI: 0000000000000001
> RBP: ffffc90000157860 R08: ffffffff92fb25f7 R09: 1ffffffff25f64be
> R10: dffffc0000000000 R11: fffffbfff25f64bf R12: dffffc0000000000
> R13: 1ffff9200002aef8 R14: ffffc900001577e0 R15: 0000000000000246
> __usb_hcd_giveback_urb+0x373/0x530 drivers/usb/core/hcd.c:1648
> usb_giveback_urb_bh+0x306/0x4e0 drivers/usb/core/hcd.c:1682
> process_one_work kernel/workqueue.c:3231 [inline]
> process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
> bh_worker+0x2a5/0x620 kernel/workqueue.c:3572
> tasklet_hi_action+0xf/0x90 kernel/softirq.c:816
> handle_softirqs+0x2d6/0x990 kernel/softirq.c:554
> run_ksoftirqd+0xca/0x130 kernel/softirq.c:928
> smpboot_thread_fn+0x544/0xa30 kernel/smpboot.c:164
> kthread+0x2f0/0x390 kernel/kthread.c:389
> ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> </TASK>
So the problem here is that __usb_hcd_giveback_urb gets called from an
interrupt that comes during a __usb_hcd_giveback_urb call from
usb_giveback_urb_bh. And KCOV annotations don't expect that
__usb_hcd_giveback_urb can be interrupted.
We had a similar issue with USB/IP before, and AFAIU the resolution
was that it's invalid to call usb_giveback_urb with interrupts enabled
[1]. But I'm not sure if the same applies to usb_giveback_urb_bh.
Alan, is this a bug in usb_giveback_urb_bh? Perhaps we need to disable
interrupts before calling __usb_hcd_giveback_urb?
Thank you!
[1] https://lore.kernel.org/linux-usb/20201006012333.GA399825@xxxxxxxxxxxxxxxxxxx/
