Re: [BUG?]3.0-rc4+ftrace+kprobe: set kprobe at instruction 'stwu' lead to system crash/freeze

On Sun, Jun 26, 2011 at 11:47:13PM +0900, Masami Hiramatsu wrote:

(2011/06/24 19:29), Steven Rostedt wrote:

quoted

On Fri, 2011-06-24 at 17:21 +0800, Yong Zhang wrote:

quoted

Hi,

When I use kprobe to do something, I found some wired thing.

When CONFIG_FUNCTION_TRACER is disabled:
(gdb) disassemble do_fork
Dump of assembler code for function do_fork:
   0xc0037390 <+0>:	mflr    r0
   0xc0037394 <+4>:	stwu    r1,-64(r1)
   0xc0037398 <+8>:	mfcr    r12
   0xc003739c <+12>:	stmw    r27,44(r1)

Then I:
modprobe kprobe_example func=do_fork offset=4
ls
Things works well.

But when CONFIG_FUNCTION_TRACER is enabled:
(gdb) disassemble do_fork
Dump of assembler code for function do_fork:
   0xc0040334 <+0>:	mflr    r0
   0xc0040338 <+4>:	stw     r0,4(r1)
   0xc004033c <+8>:	bl      0xc00109d4 <mcount>
   0xc0040340 <+12>:	stwu    r1,-80(r1)
   0xc0040344 <+16>:	mflr    r0
   0xc0040348 <+20>:	stw     r0,84(r1)
   0xc004034c <+24>:	mfcr    r12
Then I:
modprobe kprobe_example func=do_fork offset=12
ls
'ls' will never retrun. system freeze.

I'm not sure if x86 had a similar issue.

Masami, have any ideas to why this happened?

No, I don't familiar with ppc implementation. I guess
that single-step resume code failed to emulate the
instruction, but it strongly depends on ppc arch.
Maybe IBM people may know what happened.

Ananth, Jim, would you have any ideas?

On powerpc, we emulate sstep whenever possible. Only recently support to
emulate loads and stores got added. I don't have access to a powerpc box
today... but will try to recreate the problem ASAP and see what could be
happening in the presence of mcount.

Ananth