linux-kernel - Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)

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Date:	Mon, 18 Aug 2008 14:50:03 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Eran Liberty <liberty@...ricom.com>
cc:	Steven Rostedt <srostedt@...hat.com>, linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linuxppc-dev@...abs.org
Subject: Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)


On Mon, 18 Aug 2008, Eran Liberty wrote:

> Steven Rostedt wrote:
> > Eran Liberty wrote:
> > > After compiling a kernel with ftrace I started to experience all sorts of
> > > crashes.
> > 
> > Just to make sure...
> > 
> > ftrace enables markers too, and RCU has tracing with the markers. This may
> > not be the problem, but I just want to eliminate as many variables as
> > possible.
> > Could you disable ftrace, but keep the markers on too.  Also, could you
> > enable ftrace again and turn on the FTRACE_STARTUP_TEST.
> 
> for the fun of it I took out all my propriety modules; so now its a non
> tainted kernel.
> 
> Here is the matrix:
> 
> !FTRACE x !MARKERS => stable
> !FTRACE x MARKERS => stable
> FTRACE x !MARKERS => n/a (FTRACE forces MARKERS)
> FTRACE x MARKERS => unstable
> FTRACE x FTRACE_STARTUP_TEST x MARKERS => unstable + tests passed

Thanks

> 
> Testing tracer sched_switch: PASSED
> Testing tracer ftrace: PASSED
> Testing dynamic ftrace: PASSED
> 
> Oops: Exception in kernel mode, sig: 11 [#1]
> Exsw1600
> Modules linked in:
> NIP: c00bbb20 LR: c00bbb20 CTR: 00000000

Could you load this into gdb for me and show me the output of:

gdb> li *0xc00bbb20

(Assuming you compiled with debuginfo on)

and...

gdb> disass 0xc00bbb20

> REGS: dd5b1c50 TRAP: 0700   Not tainted  (2.6.27-rc2)
> MSR: 00029000 <EE,ME>  CR: 24082282  XER: 20000000
> TASK = ddcce060[1707] 'find' THREAD: dd5b0000
> GPR00: 00000000 dd5b1d00 ddcce060 dd801180 dd5b1d68 dd5b1d58 dd80125b 100234ec
> GPR08: c0800000 00019330 0000ffff dd5b1d20 24000288 100ad874 100936f8 1008a1d0
> GPR16: 10083f80 dd5b1e2c dd5b1d68 fffffff4 c0380000 dd5b1d60 dd5b1d58 dd802084
> GPR24: dc3d7700 dd802018 dd5b1d68 c0380000 dd801180 dd5b1d68 00000000 dd5b1d00
> NIP [c00bbb20] d_lookup+0x40/0x90
> LR [c00bbb20] d_lookup+0x40/0x90
> Call Trace:
> [dd5b1d00] [dd5b1d58] 0xdd5b1d58 (unreliable)
> [dd5b1d20] [c00aebc4] do_lookup+0xe8/0x220
> [dd5b1d50] [c00b0a80] __link_path_walk+0x5a4/0xd54
> [dd5b1dc0] [c00b1288] path_walk+0x58/0xe0
> [dd5b1df0] [c00b13f8] do_path_lookup+0x78/0x13c
> [dd5b1e20] [c00b20f4] user_path_at+0x64/0xac
> [dd5b1e90] [c00a9028] vfs_lstat_fd+0x34/0x74
> [dd5b1ec0] [c00a90fc] vfs_lstat+0x30/0x48
> [dd5b1ed0] [c00a9144] sys_lstat64+0x30/0x5c
> [dd5b1f40] [c0010554] ret_from_syscall+0x0/0x3c
> Instruction dump:
> 7c0802a6 bf61000c 3f60c038 7c3f0b78 90010024 7c7c1b78 7c9d2378 83db32a0
> 73c00001 7f83e378 7fa4eb78 4082002f <00000000> 2f830000 409e0030 801b32a0

Ouch! we have a 00000000 instruction. I'm almost done with the new mcount 
record for PPC (I have it done for ppc64, I'm just porting it to 32). I'm 
thinking this new code may solve your issues too. I hate the daemon.

-- Steve
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