Re: [PATCH] kcov, usb, vhost: specify contexts for remote coverage sections
From: Alan Stern <stern@rowland.harvard.edu>
Date: 2020-10-07 19:29:47
Also in:
lkml
On Wed, Oct 07, 2020 at 07:30:51PM +0200, Andrey Konovalov wrote:
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. 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 actually does 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. The approach this patch takes is to annotate every call of kcov_remote_*() callbacks with the context those callbacks are supposed to be executed in. If the current context doesn't match the mask provided to a callback, that callback is ignored. KCOV currently only supports collecting remote coverage in two contexts: task and 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 <redacted> ---
quoted hunk ↗ jump to hunk
--- a/drivers/usb/core/hcd.c +++ b/drivers/usb/core/hcd.c@@ -1646,9 +1646,9 @@ 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); + kcov_remote_start_usb((u64)urb->dev->bus->busnum, KCOV_CONTEXT_SOFTIRQ); urb->complete(urb); - kcov_remote_stop(); + kcov_remote_stop(KCOV_CONTEXT_SOFTIRQ);
This isn't right. __usb_hcd_giveback_urb() can execute in pretty much any context; its constraint is that interrupts must be disabled. Alan Stern