Currently there's a KCOV remote coverage collection section in
__usb_hcd_giveback_urb(). Initially that section was added based on the
assumption that usb_hcd_giveback_urb() can only be called in interrupt
context as indicated by a comment before it. This is what happens when
syzkaller is fuzzing the USB stack via the dummy_hcd driver.
As it turns out, it's actually valid to call usb_hcd_giveback_urb() in task
context, provided that the caller turned off the interrupts; USB/IP does
exactly that. This can lead to a nested KCOV remote coverage collection
sections both trying to collect coverage in task context. This isn't
supported by KCOV, and leads to a WARNING.
Change __usb_hcd_giveback_urb() to only call kcov_remote_*() callbacks
when it's being executed in a softirq. As the result, the coverage from
USB/IP related usb_hcd_giveback_urb() calls won't be collected, but the
WARNING is fixed.
A potential future improvement would be to support nested remote coverage
collection sections, but this patch doesn't address that.
Signed-off-by: Andrey Konovalov <andreyk...@google.com>
Acked-by: Marco Elver <el...@google.com>
---
Changes v3->v4:
- Don't make any kcov changes, do a softirq context check in usb code
instead.
---
drivers/usb/core/hcd.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index a33b849e8beb..2f6a39e09dc6 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1646,9 +1646,16 @@ static void __usb_hcd_giveback_urb(struct urb *urb)
/* pass ownership to the completion handler */
urb->status = status;
- kcov_remote_start_usb((u64)urb->dev->bus->busnum);
+ /*
+ * This function can be called in task context inside another remote
+ * coverage collection section, but KCOV doesn't support that kind of
+ * recursion yet. Only collect coverage in softirq context for now.
+ */
+ if (in_serving_softirq())
+ kcov_remote_start_usb((u64)urb->dev->bus->busnum);
urb->complete(urb);
- kcov_remote_stop();
+ if (in_serving_softirq())
+ kcov_remote_stop();
usb_anchor_resume_wakeups(anchor);
atomic_dec(&urb->use_count);
--
2.29.0.rc1.297.gfa9743e501-goog
