(2014/07/11 23:29), Josh Poimboeuf wrote:
[...]
>
>>From 951d2aec17885a62905df6b910dc705d99c63993 Mon Sep 17 00:00:00 2001
> From: Josh Poimboeuf <jpoim...@redhat.com>
> Date: Fri, 11 Jul 2014 08:58:33 -0500
> Subject: [PATCH] x86/dumpstack: fix stack traces for generated code
>
> If a function in the stack trace is dynamically generated, for example an
> ftrace dynamically generated trampoline, print_context_stack() gets confused
> and ends up showing all the following addresses as unreliable:
>
> [ 934.546013] [<ffffffff81700312>] dump_stack+0x45/0x56
> [ 934.546020] [<ffffffff8125f5b0>] ? meminfo_proc_open+0x30/0x30
> [ 934.546027] [<ffffffffa080a494>] kpatch_ftrace_handler+0x14/0xf0
> [kpatch]
> [ 934.546058] [<ffffffff812143ae>] ? seq_read+0x2de/0x3b0
> [ 934.546062] [<ffffffff812143ae>] ? seq_read+0x2de/0x3b0
> [ 934.546067] [<ffffffff8125f5b5>] ? meminfo_proc_show+0x5/0x5e0
> [ 934.546071] [<ffffffff8125f5b5>] ? meminfo_proc_show+0x5/0x5e0
> [ 934.546075] [<ffffffff8121423a>] ? seq_read+0x16a/0x3b0
> [ 934.546081] [<ffffffff8125768d>] ? proc_reg_read+0x3d/0x80
> [ 934.546088] [<ffffffff811f0668>] ? vfs_read+0x98/0x170
> [ 934.546093] [<ffffffff811f1345>] ? SyS_read+0x55/0xd0
> [ 934.546099] [<ffffffff81707969>] ? system_call_fastpath+0x16/0x1b
>
> Once it encounters an address which is not in the kernel's text area, it gets
> confused and stops updating the frame pointer.
Right, this uses a module_alloc to get a memory for trampline, but
it just allocates a page in executable vmalloc area. We need a hack
in __kernel_text_address if we really want to use that.
> The __kernel_text_address() check isn't needed when determining whether an
> address is reliable. It's only needed when deciding whether to print an
> unreliable address.
Yeah, I guess that is for the case that the frame pointer is broken.
>
> Here's the same stack trace with this patch:
>
> [ 1314.612287] [<ffffffff81700312>] dump_stack+0x45/0x56
> [ 1314.612290] [<ffffffff8125f5b0>] ? meminfo_proc_open+0x30/0x30
> [ 1314.612293] [<ffffffffa080a494>] kpatch_ftrace_handler+0x14/0xf0
> [kpatch]
> [ 1314.612306] [<ffffffffa00160c4>] 0xffffffffa00160c3
Here, this still has a wrong entry. Maybe the trampline doesn't setup
frame pointer (bp) correctly.
Thank you,
> [ 1314.612309] [<ffffffff812143ae>] ? seq_read+0x2de/0x3b0
> [ 1314.612311] [<ffffffff812143ae>] ? seq_read+0x2de/0x3b0
> [ 1314.612312] [<ffffffff8125f5b5>] ? meminfo_proc_show+0x5/0x5e0
> [ 1314.612314] [<ffffffff8125f5b5>] ? meminfo_proc_show+0x5/0x5e0
> [ 1314.612315] [<ffffffff8121423a>] ? seq_read+0x16a/0x3b0
> [ 1314.612318] [<ffffffff8125768d>] proc_reg_read+0x3d/0x80
> [ 1314.612320] [<ffffffff811f0668>] vfs_read+0x98/0x170
> [ 1314.612322] [<ffffffff811f1345>] SyS_read+0x55/0xd0
> [ 1314.612324] [<ffffffff81707969>] system_call_fastpath+0x16/0x1b
> ---
> arch/x86/kernel/dumpstack.c | 15 +++++++--------
> 1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index b74ebc7..db0a33c 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -102,14 +102,13 @@ print_context_stack(struct thread_info *tinfo,
> unsigned long addr;
>
> addr = *stack;
> - if (__kernel_text_address(addr)) {
> - if ((unsigned long) stack == bp + sizeof(long)) {
> - ops->address(data, addr, 1);
> - frame = frame->next_frame;
> - bp = (unsigned long) frame;
> - } else {
> - ops->address(data, addr, 0);
> - }
> + if ((unsigned long) stack == bp + sizeof(long)) {
> + ops->address(data, addr, 1);
> + frame = frame->next_frame;
> + bp = (unsigned long) frame;
> + print_ftrace_graph_addr(addr, data, ops, tinfo, graph);
> + } else if (__kernel_text_address(addr)) {
> + ops->address(data, addr, 0);
> print_ftrace_graph_addr(addr, data, ops, tinfo, graph);
> }
> stack++;
>
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu...@hitachi.com
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