linux-kernel - [PATCH 4.9 02/32] MIPS: Call dump_stack() from show

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Message-Id: <20180716073504.733225999@linuxfoundation.org>
Date:   Mon, 16 Jul 2018 09:36:10 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Huacai Chen <chenhc@...ote.com>, linux-mips@...ux-mips.org
Subject: [PATCH 4.9 02/32] MIPS: Call dump_stack() from show_regs()

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paul Burton <paul.burton@...s.com>

commit 5a267832c2ec47b2dad0fdb291a96bb5b8869315 upstream.

The generic nmi_cpu_backtrace() function calls show_regs() when a struct
pt_regs is available, and dump_stack() otherwise. If we were to make use
of the generic nmi_cpu_backtrace() with MIPS' current implementation of
show_regs() this would mean that we see only register data with no
accompanying stack information, in contrast with our current
implementation which calls dump_stack() regardless of whether register
state is available.

In preparation for making use of the generic nmi_cpu_backtrace() to
implement arch_trigger_cpumask_backtrace(), have our implementation of
show_regs() call dump_stack() and drop the explicit dump_stack() call in
arch_dump_stack() which is invoked by arch_trigger_cpumask_backtrace().

This will allow the output we produce to remain the same after a later
patch switches to using nmi_cpu_backtrace(). It may mean that we produce
extra stack output in other uses of show_regs(), but this:

  1) Seems harmless.
  2) Is good for consistency between arch_trigger_cpumask_backtrace()
     and other users of show_regs().
  3) Matches the behaviour of the ARM & PowerPC architectures.

Marked for stable back to v4.9 as a prerequisite of the following patch
"MIPS: Call dump_stack() from show_regs()".

Signed-off-by: Paul Burton <paul.burton@...s.com>
Patchwork: https://patchwork.linux-mips.org/patch/19596/
Cc: James Hogan <jhogan@...nel.org>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: Huacai Chen <chenhc@...ote.com>
Cc: linux-mips@...ux-mips.org
Cc: stable@...r.kernel.org # v4.9+
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/mips/kernel/process.c |    4 ++--
 arch/mips/kernel/traps.c   |    1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -641,8 +641,8 @@ static void arch_dump_stack(void *info)

 	if (regs)
 		show_regs(regs);
-
-	dump_stack();
+	else
+		dump_stack();
 }

 void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -351,6 +351,7 @@ static void __show_regs(const struct pt_
 void show_regs(struct pt_regs *regs)
 {
 	__show_regs((struct pt_regs *)regs);
+	dump_stack();
 }

 void show_registers(struct pt_regs *regs)