Commit 361aabf3 authored Jul 11, 2012 by Alan Stern Committed by Greg Kroah-Hartman Jul 16, 2012

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: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg 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;

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