Re: [PATCH] Fix Bug messages

["John Kacur" <jkacur@gmail.com>]

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On Thu, Jul 31, 2008 at 10:00 AM, Sebastien Dugue
<sebastien.dugue@bull.net> wrote:
> On Wed, 30 Jul 2008 22:48:42 +0530 Chirag Jog <chirag@linux.vnet.ibm.com> wrote:
>
>> * J?rgen Mell <j.mell@t-online.de> [2008-07-30 11:01:32]:
>>
>> > Hello Thomas,
>> >
>> > On Wednesday, 30. July 2008, Thomas Gleixner wrote:
>> > > We are pleased to announce the 2.6.26-rt1 tree, which can be
>> > > downloaded from the location:
>> >
>> > I have tried the new kernel and have some good news and some bad news:
>> >
>> > The good news: The machine boots and seems to run without major problems.
>> >
>> > The bad news: It produces continuously lots of bug messages in the error
>> > logs (cf. attached dmesg.tgz). The error at rtmutex.c:743 was already
>> > present in 2.6.25-rt* when ACPI was enabled. The 'using smp_processor_id
>> > ()  in preemptible code' is new here with 2.6.26.
>> >
>> > Machine is an old Athlon XP (single core) on an EPOX mainboard with VIA
>> > chipset.
>> >
>> > If I can help with testing, please let me know.
>> >
>> > Bye,
>> >          Jürgen
>> >
>> >
>> This patch should solve some of the bug messages.
>> It does two things:
>> 1. Change rt_runtime_lock to be a raw spinlock as the comment above it
>> says: it is nested inside the rq lock.
>>
>> 2. Change mnt_writers to be a per_cpu locked variable.
>> This eliminates the need for the codepath to disable preemption and
>> then potentially sleep, leading to the BUG messages
>>
>> Signed-Off-By: Chirag <chirag@linux.vnet.ibm.com>
>
>  Neat, the only remaining BUGs I see are from sock_prot_inuse_add()
>
> BUG: using smp_processor_id() in preemptible [00000000] code: arping/1916
> caller is .sock_prot_inuse_add+0x30/0x80
> Call Trace:
> [c0000000eed2f910] [c000000000010304] .show_stack+0x70/0x1bc (unreliable)
> [c0000000eed2f9c0] [c0000000001a2340] .debug_smp_processor_id+0x138/0x168
> [c0000000eed2fa70] [c0000000002181f4] .sock_prot_inuse_add+0x30/0x80
> [c0000000eed2fb10] [c00000000026d96c] .udp_lib_get_port+0x2a8/0x320
> [c0000000eed2fbc0] [c000000000275b30] .inet_bind+0x168/0x248
> [c0000000eed2fc60] [c000000000215024] .sys_bind+0x98/0xdc
> [c0000000eed2fd90] [c0000000002370bc] .compat_sys_socketcall+0xcc/0x214
> [c0000000eed2fe30] [c0000000000086ac] syscall_exit+0x0/0x40
> BUG: arping:1916 task might have lost a preemption check!
> Call Trace:
> [c0000000eed2f890] [c000000000010304] .show_stack+0x70/0x1bc (unreliable)
> [c0000000eed2f940] [c00000000004e298] .preempt_enable_no_resched+0x60/0x78
> [c0000000eed2f9c0] [c0000000001a2348] .debug_smp_processor_id+0x140/0x168
> [c0000000eed2fa70] [c0000000002181f4] .sock_prot_inuse_add+0x30/0x80
> [c0000000eed2fb10] [c00000000026d96c] .udp_lib_get_port+0x2a8/0x320
> [c0000000eed2fbc0] [c000000000275b30] .inet_bind+0x168/0x248
> [c0000000eed2fc60] [c000000000215024] .sys_bind+0x98/0xdc
> [c0000000eed2fd90] [c0000000002370bc] .compat_sys_socketcall+0xcc/0x214
> [c0000000eed2fe30] [c0000000000086ac] syscall_exit+0x0/0x40
>

Does this simple fix do the trick for you?

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Signed-off-by: John Kacur <jkacur@gmail.com>

Index: linux-2.6.26-rt1/net/core/sock.c
===================================================================
--- linux-2.6.26-rt1.orig/net/core/sock.c
+++ linux-2.6.26-rt1/net/core/sock.c
@@ -1943,7 +1943,7 @@ static DECLARE_BITMAP(proto_inuse_idx, P
 #ifdef CONFIG_NET_NS
 void sock_prot_inuse_add(struct net *net, struct proto *prot, int val)
 {
-	int cpu = smp_processor_id();
+	int cpu = raw_smp_processor_id();
 	per_cpu_ptr(net->core.inuse, cpu)->val[prot->inuse_idx] += val;
 }
 EXPORT_SYMBOL_GPL(sock_prot_inuse_add);