The syzbot fuzzer found that the interrupt-URB completion callback in the cdc-wdm driver was taking too long, and the driver's immediate resubmission of interrupt URBs with -EPROTO status combined with the dummy-hcd emulation to cause a CPU lockup: cdc_wdm 1-1:1.0: nonzero urb status received: -71 cdc_wdm 1-1:1.0: wdm_int_callback - 0 bytes watchdog: BUG: soft lockup - CPU#0 stuck for 26s! [syz-executor782:6625] CPU#0 Utilization every 4s during lockup: #1: 98% system, 0% softirq, 3% hardirq, 0% idle #2: 98% system, 0% softirq, 3% hardirq, 0% idle #3: 98% system, 0% softirq, 3% hardirq, 0% idle #4: 98% system, 0% softirq, 3% hardirq, 0% idle #5: 98% system, 1% softirq, 3% hardirq, 0% idle Modules linked in: irq event stamp: 73096 hardirqs last enabled at (73095): [<ffff80008037bc00>] console_emit_next_record kernel/printk/printk.c:2935 [inline] hardirqs last enabled at (73095): [<ffff80008037bc00>] console_flush_all+0x650/0xb74 kernel/printk/printk.c:2994 hardirqs last disabled at (73096): [<ffff80008af10b00>] __el1_irq arch/arm64/kernel/entry-common.c:533 [inline] hardirqs last disabled at (73096): [<ffff80008af10b00>] el1_interrupt+0x24/0x68 arch/arm64/kernel/entry-common.c:551 softirqs last enabled at (73048): [<ffff8000801ea530>] softirq_handle_end kernel/softirq.c:400 [inline] softirqs last enabled at (73048): [<ffff8000801ea530>] handle_softirqs+0xa60/0xc34 kernel/softirq.c:582 softirqs last disabled at (73043): [<ffff800080020de8>] __do_softirq+0x14/0x20 kernel/softirq.c:588 CPU: 0 PID: 6625 Comm: syz-executor782 Tainted: G W 6.10.0-rc2-syzkaller-g8867bbd4a056 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024 Testing showed that the problem did not occur if the two error messages -- the first two lines above -- were removed; apparently adding material to the kernel log takes a surprisingly large amount of time. In any case, the best approach for preventing these lockups and to avoid spamming the log with thousands of error messages per second is to ratelimit the two dev_err() calls. Therefore we replace them with dev_err_ratelimited(). Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Suggested-by: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> Reported-and-tested-by: syzbot+5f996b83575ef4058638@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lore.kernel.org/linux-usb/00000000000073d54b061a6a1c65@xxxxxxxxxx/ Reported-and-tested-by: syzbot+1b2abad17596ad03dcff@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lore.kernel.org/linux-usb/000000000000f45085061aa9b37e@xxxxxxxxxx/ Fixes: 9908a32e94de ("USB: remove err() macro from usb class drivers") Link: https://lore.kernel.org/linux-usb/40dfa45b-5f21-4eef-a8c1-51a2f320e267@xxxxxxxxxxxxxxxxxxx/ Cc: stable@xxxxxxxxxxxxxxx --- drivers/usb/class/cdc-wdm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) Index: usb-devel/drivers/usb/class/cdc-wdm.c =================================================================== --- usb-devel.orig/drivers/usb/class/cdc-wdm.c +++ usb-devel/drivers/usb/class/cdc-wdm.c @@ -266,14 +266,14 @@ static void wdm_int_callback(struct urb dev_err(&desc->intf->dev, "Stall on int endpoint\n"); goto sw; /* halt is cleared in work */ default: - dev_err(&desc->intf->dev, + dev_err_ratelimited(&desc->intf->dev, "nonzero urb status received: %d\n", status); break; } } if (urb->actual_length < sizeof(struct usb_cdc_notification)) { - dev_err(&desc->intf->dev, "wdm_int_callback - %d bytes\n", + dev_err_ratelimited(&desc->intf->dev, "wdm_int_callback - %d bytes\n", urb->actual_length); goto exit; }
