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Commit 361aabf3 authored by Alan Stern's avatar Alan Stern Committed by Greg Kroah-Hartman
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USB: EHCI: don't lose events during a scan 



This patch (as1584) fixes a minor bug that has been present in
ehci-hcd since the beginning.

Scanning the schedules for URB completions is single-threaded.  If a
completion interrupt occurs while an URB is being given back, the
interrupt handler realizes that a scan is in progress on another CPU
and avoids starting a new one.

This means that completion events can be lost.  If an URB completes
after it has been scanned but while a scan is still in progress, the
driver won't notice and won't rescan the completed URB.

The patch fixes the problem by adding a new flag to indicate that
another scan is needed after the current scan is done.  The flag gets
set whenever a completion interrupt occurs while a scan is in
progress.  The rescan will see the completion, thus preventing it from
getting lost.

Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 32830f20

drivers/usb/host/ehci-hcd.c

+10 −3
Original line number Diff line number Diff line
@@ -400,14 +400,21 @@ static void ehci_work (struct ehci_hcd *ehci) 
	 * it reports urb completions.  this flag guards against bogus

	 * attempts at re-entrant schedule scanning.

	 */

	if (ehci->scanning)

	if (ehci->scanning) {

		ehci->need_rescan = true;

		return;

	ehci->scanning = 1;

	}

	ehci->scanning = true;



 rescan:

	ehci->need_rescan = false;

	if (ehci->async_count)

		scan_async(ehci);

	if (ehci->next_uframe != -1)

		scan_periodic (ehci);

	ehci->scanning = 0;

	if (ehci->need_rescan)

		goto rescan;

	ehci->scanning = false;



	/* the IO watchdog guards against hardware or driver bugs that

	 * misplace IRQs, and should let us run completely without IRQs.

drivers/usb/host/ehci.h

+2 −1
Original line number Diff line number Diff line
@@ -113,7 +113,8 @@ struct ehci_hcd { /* one per controller */ 
	enum ehci_rh_state	rh_state;



	/* general schedule support */

	unsigned		scanning:1;

	bool			scanning:1;

	bool			need_rescan:1;

	bool			intr_unlinking:1;

	bool			async_unlinking:1;