Fw: BUG: atomic counter underflow when running "rmmod tg3" on 2.6.10-rc1-mm3

Fw: BUG: atomic counter underflow when running "rmmod tg3" on 2.6.10-rc1-mm3

[Andrew Morton]

There's a debug patch in -mm which generates a trace when someone does
atomic_dec_and_test() on an atomic_t which already has a value of zero.

ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.10-rc1/2.6.10-rc1-mm3/broken-out/detect-atomic-counter-underflows.patch

It looks like it has found a problem in qdisc_destroy().



Begin forwarded message:

Date: Tue, 9 Nov 2004 03:33:36 +0100
From: Bernhard Rosenkraenzer <bero@arklinux.org>
To: linux-kernel@vger.kernel.org
Subject: BUG: atomic counter underflow when running "rmmod tg3" on 2.6.10-rc1-mm3


BUG: atomic counter underflow at:
 [<c02882f6>] qdisc_destroy+0x66/0x80
 [<c02885e2>] dev_shutdown+0x32/0x90
 [<c02d796f>] __down_failed_trylock+0x7/0xc
 [<c027b6b2>] unregister_netdevice+0x142/0x29e
 [<c014c171>] handle_mm_fault+0xf1/0x510
 [<c0240a95>] unregister_netdev+0x15/0x20
 [<e0d3a2b5>] tg3_remove_one+0x25/0x70 [tg3]
 [<c01db4e9>] pci_device_remove+0x69/0x70
 [<c0232646>] device_release_driver+0x86/0x90
 [<c0232a2b>] bus_remove_driver+0x5b/0x100
 [<e0d3a780>] tg3_cleanup+0x0/0x13 [tg3]
 [<c0232fc0>] driver_unregister+0x10/0x20
 [<c01db234>] pci_unregister_driver+0x14/0xa0
 [<e0d3a78f>] tg3_cleanup+0xf/0x13 [tg3]
 [<c013462b>] sys_delete_module+0x17b/0x1e0
 [<c0104ff1>] sysenter_past_esp+0x52/0x71
divert: freeing divert_blk for eth0

Re: Fw: BUG: atomic counter underflow when running "rmmod tg3" on 2.6.10-rc1-mm3

[Patrick McHardy]

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Andrew Morton wrote:

>There's a debug patch in -mm which generates a trace when someone does
>atomic_dec_and_test() on an atomic_t which already has a value of zero.
>
>ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.10-rc1/2.6.10-rc1-mm3/broken-out/detect-atomic-counter-underflows.patch
>
>It looks like it has found a problem in qdisc_destroy().
>  
>
Already fixed in latest -bk by the attached patch. The builtin qdiscs
are not refcounted, but qdisc_destroy treated them as other qdiscs.

Regards
Patrick


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# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
#   2004/11/05 16:30:34-08:00 tgraf@suug.ch 
#   [PKT_SCHED]: Builtin qdiscs should avoid all qdisc_destroy() processing.
#   
#   None of the code in __qdisc_destroy should be applied to a builtin qdisc
#   or am I missing something?
#   
#   The patch below prevents builtin qdiscs from being destroyed and
#   fixes a refcnt underflow whould lead to a bogus list unlinking
#   and dev_put.
#   
#   Signed-off-by: Thomas Graf <tgraf@suug.ch>
#   Signed-off-by: David S. Miller <davem@davemloft.net>
# 
# net/sched/sch_generic.c
#   2004/11/05 16:30:14-08:00 tgraf@suug.ch +3 -3
#   [PKT_SCHED]: Builtin qdiscs should avoid all qdisc_destroy() processing.
#   
#   None of the code in __qdisc_destroy should be applied to a builtin qdisc
#   or am I missing something?
#   
#   The patch below prevents builtin qdiscs from being destroyed and
#   fixes a refcnt underflow whould lead to a bogus list unlinking
#   and dev_put.
#   
#   Signed-off-by: Thomas Graf <tgraf@suug.ch>
#   Signed-off-by: David S. Miller <davem@davemloft.net>
# 
diff -Nru a/net/sched/sch_generic.c b/net/sched/sch_generic.c
--- a/net/sched/sch_generic.c	2004-11-09 06:50:10 +01:00
+++ b/net/sched/sch_generic.c	2004-11-09 06:50:10 +01:00
@@ -479,15 +479,15 @@
 	module_put(ops->owner);
 
 	dev_put(qdisc->dev);
-	if (!(qdisc->flags&TCQ_F_BUILTIN))
-		kfree((char *) qdisc - qdisc->padded);
+	kfree((char *) qdisc - qdisc->padded);
 }
 
 /* Under dev->queue_lock and BH! */
 
 void qdisc_destroy(struct Qdisc *qdisc)
 {
-	if (!atomic_dec_and_test(&qdisc->refcnt))
+	if (qdisc->flags & TCQ_F_BUILTIN ||
+		!atomic_dec_and_test(&qdisc->refcnt))
 		return;
 	list_del(&qdisc->list);
 	call_rcu(&qdisc->q_rcu, __qdisc_destroy);