list corruption on removal of snd_seq_dummy

[Dave Jones <davej@redhat.com>]

If you apply the debugging patch below (based on one from -mm)
and rmmod snd_seq_dummy, you get this spew:
(based on a 2.6.17rc6 kernel, but likely still there in todays -git)

The code in question is doing..

        __list_add(&deleted_list,
               client->ports_list_head.prev,
               client->ports_list_head.next);

which looks fishy, as those two elements aren't going to be consecutive,
as __list_add expects.

		Dave

List corruption. next->prev should be f76896e8, but was f70acbcc
------------[ cut here ]------------
kernel BUG at include/linux/list.h:58!
invalid opcode: 0000 [#1]
SMP
last sysfs file: /devices/pci0000:00/0000:00:1f.3/i2c-0/0-002e/pwm3
Modules linked in: lm85 hwmon_vid hwmon i2c_isa ipv6 nls_utf8 loop snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss matroxfb_base matroxfb_DAC1064 snd_mixer_oss matroxfb_accel matroxfb_Ti3026 matroxfb_g450 g450_pll matroxfb_misc snd_pcm 3w_9xxx e1000 snd_timer snd i2c_i801 soundcore i2c_core snd_page_alloc ext3 jbd 3w_xxxx ata_piix libata sd_mod scsi_mod
CPU:    1
EIP:    0060:[<f8a1a56d>]    Not tainted VLI
EFLAGS: 00010092   (2.6.16-1.2232_FC6 #1)
EIP is at snd_seq_delete_all_ports+0x57/0x167 [snd_seq]
eax: 00000044   ebx: f76896e8   ecx: c06c77d0   edx: 00000096
esi: f76896e8   edi: f70acbcc   ebp: f70acb50   esp: f772cf08
ds: 007b   es: 007b   ss: 0068
Process rmmod (pid: 6274, threadinfo=f772c000 task=df26f550)
Stack: f8a1b83b f76896e8 f70acbcc f70acbe4 f70acbd4 00000282 22222222 22222222
       f70acb50 00000020 00000000 f772c000 f8a1521e f70acb50 f8a152e2 c043df66
       f772c000 c0445bf0 f70acb50 f8a1778b f89b4e00 c043e177 5f646e73 5f716573
Call Trace:
 <f8a1521e> seq_free_client1+0x8/0x90 [snd_seq]  <f8a152e2> seq_free_client+0x3c/0x78 [snd_seq]
 <c043df66> __try_stop_module+0x0/0x44  <c0445bf0> stop_machine_run+0x2e/0x34
 <f8a1778b> snd_seq_delete_kernel_client+0x1a/0x2c [snd_seq]  <c043e177> sys_delete_module+0x192/0x1bb
 <c060f020> do_page_fault+0x235/0x5ba  <c045ab3f> do_munmap+0x196/0x1af
 <c0403e1f> syscall_call+0x7/0xb
Code: 24 14 39 7d 7c 74 67 8b 5d 7c 8b b5 80 00 00 00 8b 43 04 39 f0 74 1c 89 74 24 04 89 44 24 08 c7 04 24 3b b8 a1 f8 e8 e7 ab a0 c7 <0f> 0b 3a 00 26 b8 a1 f8 8b 06 39 d8 74 1c 89 5c 24 04 89 44 24
EIP: [<f8a1a56d>] snd_seq_delete_all_ports+0x57/0x167 [snd_seq] SS:ESP 0068:f772cf08
 <3>BUG: sleeping function called from invalid context at include/linux/rwsem.h:43
in_atomic():0, irqs_disabled():1
 <c042ffa2> blocking_notifier_call_chain+0x18/0x4b  <c0427387> do_exit+0x19/0x7a5
 <c053a76b> do_unblank_screen+0x2a/0x127  <c040549a> die+0x2a5/0x2ca
 <c0405b30> do_invalid_op+0x0/0xab  <c0405bd2> do_invalid_op+0xa2/0xab
 <f8a1a56d> snd_seq_delete_all_ports+0x57/0x167 [snd_seq]  <c041e25f> find_busiest_group+0xfc/0x29c
 <c060dfd0> _spin_unlock_irq+0x5/0x7  <c04390ef> debug_mutex_add_waiter+0x97/0xa9
 <f8a1a531> snd_seq_delete_all_ports+0x1b/0x167 [snd_seq]  <c04049b7> error_code+0x4f/0x54
 <f8a1a56d> snd_seq_delete_all_ports+0x57/0x167 [snd_seq]  <f8a1521e> seq_free_client1+0x8/0x90 [snd_seq]
 <f8a152e2> seq_free_client+0x3c/0x78 [snd_seq]  <c043df66> __try_stop_module+0x0/0x44
 <c0445bf0> stop_machine_run+0x2e/0x34  <f8a1778b> snd_seq_delete_kernel_client+0x1a/0x2c [snd_seq]
 <c043e177> sys_delete_module+0x192/0x1bb  <c060f020> do_page_fault+0x235/0x5ba
 <c045ab3f> do_munmap+0x196/0x1af  <c0403e1f> syscall_call+0x7/0xb
BUG: rmmod/6274, lock held at task exit time!
 [f8a21fa0] {register_mutex}
.. held by:             rmmod: 6274 [df26f550, 117]
... acquired at:               seq_free_client+0x10/0x78 [snd_seq]



--- linux-2.6.12/include/linux/list.h~	2005-08-08 15:34:50.000000000 -0400
+++ linux-2.6.12/include/linux/list.h	2005-08-08 15:35:22.000000000 -0400
@@ -5,7 +5,9 @@
 
 #include <linux/stddef.h>
 #include <linux/prefetch.h>
+#include <linux/kernel.h>
 #include <asm/system.h>
+#include <asm/bug.h>
 
 /*
  * These are non-NULL pointers that will result in page faults
@@ -52,6 +52,16 @@ static inline void __list_add(struct lis
 			      struct list_head *prev,
 			      struct list_head *next)
 {
+	if (next->prev != prev) {
+		printk("List corruption. next->prev should be %p, but was %p\n",
+				prev, next->prev);
+		BUG();
+	}
+	if (prev->next != next) {
+		printk("List corruption. prev->next should be %p, but was %p\n",
+				next, prev->next);
+		BUG();
+	}
 	next->prev = new;
 	new->next = next;
 	new->prev = prev;
@@ -162,6 +162,16 @@ static inline void __list_del(struct lis
  */
 static inline void list_del(struct list_head *entry)
 {
+	if (entry->prev->next != entry) {
+		printk("List corruption. prev->next should be %p, but was %p\n",
+				entry, entry->prev->next);
+		BUG();
+	}
+	if (entry->next->prev != entry) {
+		printk("List corruption. next->prev should be %p, but was %p\n",
+				entry, entry->next->prev);
+		BUG();
+	}
 	__list_del(entry->prev, entry->next);
 	entry->next = LIST_POISON1;
 	entry->prev = LIST_POISON2;


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