linux-kernel - [tip:x86/mm] x86/dumpstack: Try harder to get a call trace on stack overflow

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Date:	Fri, 15 Jul 2016 05:00:56 -0700
From:	tip-bot for Andy Lutomirski <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	dvlasenk@...hat.com, hpa@...or.com, mingo@...nel.org,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	luto@...nel.org, bp@...en8.de, torvalds@...ux-foundation.org,
	jpoimboe@...hat.com, tglx@...utronix.de, brgerst@...il.com
Subject: [tip:x86/mm] x86/dumpstack: Try harder to get a call trace on stack
 overflow

Commit-ID:  9a2e9da3e003112399f2863b7b6b911043c01895
Gitweb:     http://git.kernel.org/tip/9a2e9da3e003112399f2863b7b6b911043c01895
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Thu, 14 Jul 2016 13:22:52 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 15 Jul 2016 10:26:26 +0200

x86/dumpstack: Try harder to get a call trace on stack overflow

If we overflow the stack, print_context_stack() will abort.  Detect
this case and rewind back into the valid part of the stack so that
we can trace it.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/ee1690eb2715ccc5dc187fde94effa4ca0ccbbcd.1468527351.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/dumpstack.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index ef8017c..cc88e25 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -87,7 +87,7 @@ static inline int valid_stack_ptr(struct task_struct *task,
 		else
 			return 0;
 	}
-	return p > t && p < t + THREAD_SIZE - size;
+	return p >= t && p < t + THREAD_SIZE - size;
 }
 
 unsigned long
@@ -98,6 +98,14 @@ print_context_stack(struct task_struct *task,
 {
 	struct stack_frame *frame = (struct stack_frame *)bp;
 
+	/*
+	 * If we overflowed the stack into a guard page, jump back to the
+	 * bottom of the usable stack.
+	 */
+	if ((unsigned long)task_stack_page(task) - (unsigned long)stack <
+	    PAGE_SIZE)
+		stack = (unsigned long *)task_stack_page(task);
+
 	while (valid_stack_ptr(task, stack, sizeof(*stack), end)) {
 		unsigned long addr;