From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: linuxppc-dev@ozlabs.org, Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH] powerpc/64: Fix stacktrace on BE when function_graph is enabled
Date: Sat, 24 Aug 2019 14:29:17 +0530 [thread overview]
Message-ID: <1566636816.4snngx2qd3.naveen@linux.ibm.com> (raw)
In-Reply-To: <20190823122901.32667-1-mpe@ellerman.id.au>
Michael Ellerman wrote:
> Currently if we oops or warn while function_graph is active the stack
> trace looks like:
> .trace_graph_return+0xac/0x100
> .ftrace_return_to_handler+0x98/0x140
> .return_to_handler+0x20/0x40
> .return_to_handler+0x0/0x40
> .return_to_handler+0x0/0x40
> .return_to_handler+0x0/0x40
> .return_to_handler+0x0/0x40
> .return_to_handler+0x0/0x40
> .return_to_handler+0x0/0x40
> .cpu_startup_entry+0x34/0x40
> .start_secondary+0x680/0x6f0
> start_secondary_prolog+0x10/0x14
>
> Notice the multiple entries that just show .return_to_handler.
>
> There is logic in show_stack() to detect this case and print the
> traced function, but we inadvertently broke it in commit
> 7d56c65a6ff9 ("powerpc/ftrace: Remove mod_return_to_handler") (2014),
> because that commit accidentally removed the dereference of rth which
> gets the text address from the function descriptor. Hence this is only
> broken on big endian (or technically ELFv1).
>
> Fix it by using the proper accessor, which is ppc_function_entry().
> Result is we get a stack trace such as:
>
> .trace_graph_return+0x134/0x160
> .ftrace_return_to_handler+0x94/0x140
> .return_to_handler+0x20/0x40
> .return_to_handler+0x0/0x40 (.shared_cede_loop+0x48/0x130)
> .return_to_handler+0x0/0x40 (.cpuidle_enter_state+0xa0/0x690)
> .return_to_handler+0x0/0x40 (.cpuidle_enter+0x44/0x70)
> .return_to_handler+0x0/0x40 (.call_cpuidle+0x68/0xc0)
> .return_to_handler+0x0/0x40 (.do_idle+0x37c/0x400)
> .return_to_handler+0x0/0x40 (.cpu_startup_entry+0x30/0x50)
> .rest_init+0x224/0x348
>
> Fixes: 7d56c65a6ff9 ("powerpc/ftrace: Remove mod_return_to_handler")
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
> arch/powerpc/kernel/process.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 8fc4de0d22b4..1601d7cfe45e 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -2048,7 +2048,7 @@ void show_stack(struct task_struct *tsk, unsigned long *stack)
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> struct ftrace_ret_stack *ret_stack;
> extern void return_to_handler(void);
> - unsigned long rth = (unsigned long)return_to_handler;
> + unsigned long rth = ppc_function_entry(return_to_handler);
Thanks! This looks good to me. A small suggestion though -- can we use
dereference_kernel_function_descriptor() instead? It will be a nop for
ABIv2, which would be nice, but not really a major deal.
In either case:
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
- Naveen
next prev parent reply other threads:[~2019-08-24 9:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-23 12:29 [PATCH] powerpc/64: Fix stacktrace on BE when function_graph is enabled Michael Ellerman
2019-08-24 8:59 ` Naveen N. Rao [this message]
2019-09-05 9:53 ` Michael Ellerman
2019-09-05 11:35 ` Naveen N. Rao
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1566636816.4snngx2qd3.naveen@linux.ibm.com \
--to=naveen.n.rao@linux.vnet.ibm.com \
--cc=linuxppc-dev@ozlabs.org \
--cc=mpe@ellerman.id.au \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).