linux-kernel - Re: [BUG] usb/core/hub.c loops forever on resume from ram due to bluetooth

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Date:	Tue, 08 May 2007 09:53:05 -0400
From:	Mark Lord <lkml@....ca>
To:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...e.de>, Andrew Morton <akpm@...l.org>
Cc:	marcel@...tmann.org
Subject: Re: [BUG] usb/core/hub.c loops forever on resume from ram due to
 bluetooth

Greg ?

The oddball thing here is that on a UP machine with a UP kernel,
this (below) was never an issue.

After moving the drive to a dual-core machine and rebuilding
the kernel with SMP=y, the problem becomes a killer here.
The two machines are nearly identical, apart from the CPUs.

The failing machine is a Dell Inspiron 9400,
and mine isn't the only unit that has this issue.

----------Original message:

I have just replaced my primary single-core notebook
with a nearly identical dual-core notebook,
and moved the usb-bluetooth peripheral from the old
machine to the new one.

On the single-core machine, suspend/resume (RAM) worked
fine even with the bluetooth module enabled.

On the new dual-core machine, resuming with bluetooth
enabled results in an infinite(?) lockup in an unbounded
loop in hub_tt_kevent().  With PM debug on, I see
tens of thousands of these messages scrolling on the console:

    kernel: usb 5-1: clear tt 4 (9042) error -71
    kernel: usb 5-1: clear tt 4 (9042) error -71
    kernel: usb 5-1: clear tt 4 (9042) error -71
    (over and over and ...)

By restricting iterations on the unbounded loop
the machine is able to resume again.

Greg / Marcel: any words of wisdom?

And we should probably put bounds permanently on that loop:

I devised/used this patch to accomplish it.
Now, I still get close to a thousand or so such
messages, in groups, showing up in syslog,
but at least the system can resume after suspend.

Signed-off-by:  Mark Lord <mlord@...ox.com>

--- linux/drivers/usb/core/hub.c.orig    2007-04-26 12:02:47.000000000 -0400
+++ linux/drivers/usb/core/hub.c    2007-05-01 18:48:46.000000000 -0400
@@ -403,9 +403,10 @@
    struct usb_hub        *hub =
        container_of(work, struct usb_hub, tt.kevent);
    unsigned long        flags;
+    int            limit = 500;

    spin_lock_irqsave (&hub->tt.lock, flags);
-    while (!list_empty (&hub->tt.clear_list)) {
+    while (--limit && !list_empty (&hub->tt.clear_list)) {
        struct list_head    *temp;
        struct usb_tt_clear    *clear;
        struct usb_device    *hdev = hub->hdev;
-----

-
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