Bug 736815

Summary:	Code dump in kernel oops reports is sometimes truncated
Product:	[Fedora] Fedora	Reporter:	Chuck Ebbert <cebbert>
Component:	kernel	Assignee:	Kay Sievers <kay>
Status:	CLOSED ERRATA	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	16	CC:	gansalmon, itamar, jonathan, kernel-maint, madhu.chinakonda, tcallawa
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Hardware:	Unspecified
OS:	Unspecified
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Fixed In Version:		Doc Type:	Bug Fix
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Clone Of:		Environment:
Last Closed:	2012-03-28 00:57:43 UTC	Type:	---
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:

Description Chuck Ebbert 2011-09-08 18:56:41 UTC

Sometimes the code dump in kernel oops reports gets truncated, like this:

Code: 31 c0 5d c3 55 48 89 e5 41 54 53 66 66 66 66 90 41 89 d4 48 89 fb 41 c1 e4 09 85 f6 75 0a 44 3b 67 30 0f 84 d1 00 00 00 48 63 c6 

There should be a 1-byte insn value in braces, like <30>, followed by more plain values.

Other times the entire line is shown:

Code: e5 66 66 66 66 90 b8 00 00 01 00 f0 0f c1 07 0f b7 d0 c1 e8 10 39 c2 74 07 f3 90 0f b7 17 eb f5 5d c3 55 48 89 e5 66 66 66 66 90 <8b> 07 89 c2 c1 c0 10 39 c2 8d 90 00 00 01 00 75 04 f0 0f b1 17

It seems to depend on the value in the brackets.

Looks like this is caused by:

commit 9d90c8d9cde929cbc575098e825d7c29d9f45054
"printk: do not mangle valid userspace syslog prefixes"

This part of that patch looks wrong, but that may not be the whole story:

+    if (p[1] < '0' && p[1] > '9')
+      return 0;

Comment 1 Kay Sievers 2011-12-06 20:50:41 UTC

That looks like something to fix in the dumping code:
  arch/x86/kernel/dumpstack_64.c
    printk("<%02x> ", c);

Printk lines are not allowed to start with the syslog prefix <number>.
It only worked in earlier versions because the kernel supported
single digits only, which probably nobody has enclosed in <>.

I guess the separating ' ' between the fields in the output loop needs to
be moved to prefix the line and not be appended, so that the printk parser
does not detect a level prefix.

Alternatively it might be sufficient to add KERN_INFO in front, so that
a valid prefix is always there and gets stripped by printk.

Comment 2 Dave Jones 2011-12-06 21:11:23 UTC

But this isn't at the start of a line. The start of the line is "<KERN_EMERG> Code: "

Comment 3 Kay Sievers 2011-12-06 21:31:25 UTC

The current (simple) implementation of printk() does not have a concept of
a new line for the input, only for the output. The syslog prefix is checked
with every invocation of printk().

It was like that before the above mentioned change already, it's just that
nobody ever printed '<[0-9]>' and expected it to show up in the log. Now with
the (proper) multi-digit support it seams to eat the <[0-9][0-9]> matches.

The newline logic in printk is a global variable, so any other user finish
the line in-between multiple printk()s.

I guess the best option is to change the caller to print with a leading ' '?

Comment 4 Kay Sievers 2011-12-06 21:33:51 UTC

There is also the KERN_CONT prefix magic, which might just do the right thing
here.

Comment 5 Chuck Ebbert 2011-12-07 14:38:30 UTC

I'll change it to use leading spaces, that looks easy enough to do.

Comment 6 Chuck Ebbert 2011-12-07 15:15:42 UTC

I've put a fix in rawhide for now.

Comment 7 Josh Boyer 2011-12-19 21:28:33 UTC

This looks like it's been fixed upstream:

http://git.kernel.org/?p=linux/kernel/git/tip/tip.git;a=commitdiff;h=13f541c10b30fc6529200d7f9a0073217709622f

Seems the KERN_CONT route is how they went.

Comment 8 Dave Jones 2011-12-20 00:04:04 UTC

changed in git to use that version. also added to f15/f16.

Comment 9 Dave Jones 2012-03-22 16:53:33 UTC

[mass update]
kernel-3.3.0-4.fc16 has been pushed to the Fedora 16 stable repository.
Please retest with this update.

Comment 10 Dave Jones 2012-03-22 16:57:17 UTC

[mass update]
kernel-3.3.0-4.fc16 has been pushed to the Fedora 16 stable repository.
Please retest with this update.

Comment 11 Dave Jones 2012-03-22 17:08:24 UTC

[mass update]
kernel-3.3.0-4.fc16 has been pushed to the Fedora 16 stable repository.
Please retest with this update.