linux-kernel - Re: 3.13: BUG: unable to handle kernel paging request at 00000000b4343e88

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Date:	Mon, 27 Jan 2014 16:53:53 +0100
From:	Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
To:	Meelis Roos <mroos@...ux.ee>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: 3.13: BUG: unable to handle kernel paging request at 00000000b4343e88

On 24.01.2014 21:54, Meelis Roos wrote:
>>>> It looks like gcov exploded when running a module's constructors or
>>>> init function, but I'm unable to work out which module it was :(
>>> [...]
>>>
>>>> Maybe it's tg3.
>>>>
>>>> Could you add `ignore_loglevel' to the kernel boot parameters?  That
>>>> should make all pr_debug()s come out and they include the module's
>>>> name.
>>
>> I'm not sure if this related, but all 3 kernel logs consistently contain
>> this error message:
>>
>>> [    0.617401] gcov: could not create file
>>
>> which should only be shown in case of severe out-of-memory situations or
>> duplicate object file names.
>>
>> Could you retry with the following patch applied (2 times if possible)
>> and send dmesg output?
> 
> This seems to be relevant - now there is a reproducible crash during the 
> printk. Captured end of the backtrace from HP ILO as image, attached. 
> This is reproducible.

Ok, that's a lead. It appears that gcov-kernel receives gcov_info
structures in an unexpected format. Based on your previous dmesg output,
your kernel was compiled using gcc 4.7.2 which gcov-kernel should be able
to handle just fine. Could you please try out this debugging patch
(replacing the previous one)? Output will likely be quite verbose, so you
might consider using log_buf_len=1M or similar as kernel parameter.

-----
diff -Naurp a/kernel/gcov/base.c b/kernel/gcov/base.c
--- a/kernel/gcov/base.c
+++ b/kernel/gcov/base.c
@@ -18,6 +18,7 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/printk.h>
 #include "gcov.h"

 static int gcov_events_enabled;
@@ -31,6 +32,9 @@ void __gcov_init(struct gcov_info *info)
 {
 	static unsigned int gcov_version;

+	pr_warn("__gcov_init(%p): enter\n", info);
+	print_hex_dump(KERN_WARNING, "", DUMP_PREFIX_ADDRESS, 16, 4, info,
+		       64, true);
 	mutex_lock(&gcov_lock);
 	if (gcov_version == 0) {
 		gcov_version = gcov_info_version(info);
@@ -48,6 +52,7 @@ void __gcov_init(struct gcov_info *info)
 	if (gcov_events_enabled)
 		gcov_event(GCOV_ADD, info);
 	mutex_unlock(&gcov_lock);
+	pr_warn("__gcov_init(%p): exit\n", info);
 }
 EXPORT_SYMBOL(__gcov_init);

diff -Naurp a/kernel/module.c b/kernel/module.c
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3003,8 +3003,11 @@ static void do_mod_ctors(struct module *
 #ifdef CONFIG_CONSTRUCTORS
 	unsigned long i;

-	for (i = 0; i < mod->num_ctors; i++)
+	for (i = 0; i < mod->num_ctors; i++) {
+		pr_warn("Calling mod(%s)->ctors[%d]=%p\n", mod->name, i,
+			mod->ctors[i]);
 		mod->ctors[i]();
+	}
 #endif
 }

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