linuxppc-dev.lists.ozlabs.org archive mirror
 help / color / mirror / Atom feed
From: Michael Ellerman <mpe@ellerman.id.au>
To: linuxppc-dev@ozlabs.org
Subject: [PATCH] powerpc/64: Fix stacktrace on BE when function_graph is enabled
Date: Fri, 23 Aug 2019 22:29:01 +1000	[thread overview]
Message-ID: <20190823122901.32667-1-mpe@ellerman.id.au> (raw)

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);
 	int curr_frame = 0;
 #endif
 
-- 
2.21.0


             reply	other threads:[~2019-08-23 12:32 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-23 12:29 Michael Ellerman [this message]
2019-08-24  8:59 ` [PATCH] powerpc/64: Fix stacktrace on BE when function_graph is enabled Naveen N. Rao
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=20190823122901.32667-1-mpe@ellerman.id.au \
    --to=mpe@ellerman.id.au \
    --cc=linuxppc-dev@ozlabs.org \
    /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).