Re: [ftrace/fgraph/x86] BUG: unable to handle kernel paging request at 3d00c17d

From: Steven Rostedt
Date: Wed Dec 10 2014 - 23:09:35 EST

On Wed, 10 Dec 2014 15:17:32 -0800
Fengguang Wu <fengguang.wu@xxxxxxxxx> wrote:

> Hi Steven,
> 0day kernel testing robot got the below dmesg and the first bad commit is
> git:// master
> commit 6a06bdbf7f9c669743f58084991ba280f2925586
> Author: Steven Rostedt (Red Hat) <rostedt@xxxxxxxxxxx>
> AuthorDate: Mon Nov 24 21:00:34 2014 -0500
> Commit: Steven Rostedt <rostedt@xxxxxxxxxxx>
> CommitDate: Mon Dec 1 14:08:58 2014 -0500
> ftrace/fgraph/x86: Have prepare_ftrace_return() take ip as first parameter
> The function graph helper function prepare_ftrace_return() which does the work
> to hijack the parent pointer has that parent pointer as its first parameter.
> Instead, if we make it the second parameter and have ip as the first parameter
> (self_addr), then it can use the %rdi from save_mcount_regs that loads it
> already.
> Link:
> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

Crap! Yeah, I was wondering how this could be the bug, but then I
realized this was i386 not x86_64 and I never updated the i386 call to

Does this patch fix it?

-- Steve

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index b553ed89e5f5..df3e608d409b 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1192,10 +1192,10 @@ ENTRY(ftrace_graph_caller)
pushl %eax
pushl %ecx
pushl %edx
- movl 0xc(%esp), %edx
- lea 0x4(%ebp), %eax
+ movl 0xc(%esp), %eax
+ lea 0x4(%ebp), %edx
movl (%ebp), %ecx
- subl $MCOUNT_INSN_SIZE, %edx
+ subl $MCOUNT_INSN_SIZE, %eax
call prepare_ftrace_return
popl %edx
popl %ecx
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