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Subject[tip:x86/urgent] x86/unwinder/guess: Prevent using CONFIG_UNWINDER_GUESS=y with CONFIG_STACKDEPOT=y
Commit-ID:  0a373d4fc248cb707821d7dad54ce6d5bcb0cdfe
Gitweb: https://git.kernel.org/tip/0a373d4fc248cb707821d7dad54ce6d5bcb0cdfe
Author: Andrey Ryabinin <aryabinin@virtuozzo.com>
AuthorDate: Thu, 30 Nov 2017 15:35:54 +0300
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 11 Dec 2017 19:07:07 +0100

x86/unwinder/guess: Prevent using CONFIG_UNWINDER_GUESS=y with CONFIG_STACKDEPOT=y

Stackdepot doesn't work well with CONFIG_UNWINDER_GUESS=y.
The 'guess' unwinder generate awfully large and inaccurate stacktraces,
thus stackdepot can't deduplicate stacktraces because they all look like
unique. Eventually stackdepot reaches its capacity limit:

WARNING: CPU: 0 PID: 545 at lib/stackdepot.c:119 depot_save_stack+0x28e/0x550
Call Trace:
? kasan_kmalloc+0x144/0x160
? depot_save_stack+0x1f5/0x550
? do_raw_spin_unlock+0xda/0xf0
? preempt_count_sub+0x13/0xc0

<...90 lines...>

? do_raw_spin_unlock+0xda/0xf0

Add a STACKDEPOT=n dependency to UNWINDER_GUESS to avoid the problem.

Reported-by: kernel test robot <xiaolong.ye@intel.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171130123554.4330-1-aryabinin@virtuozzo.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/Kconfig.debug | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 6293a87..672441c 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -400,6 +400,7 @@ config UNWINDER_FRAME_POINTER
config UNWINDER_GUESS
bool "Guess unwinder"
depends on EXPERT
+ depends on !STACKDEPOT
---help---
This option enables the "guess" unwinder for unwinding kernel stack
traces. It scans the stack and reports every kernel text address it
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