linux-kernel - [PATCH 2/2] x86/unwind: Dump all stacks in unwind

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Message-Id: <016d6a9810d7d1bfc87ef8c0e6ee041c6744c909.1493171120.git.jpoimboe@redhat.com>
Date:   Tue, 25 Apr 2017 20:48:52 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] x86/unwind: Dump all stacks in unwind_dump()

Currently unwind_dump() dumps only the most recently accessed stack.
But it has a few issues.

In some cases, 'first_sp' can get out of sync with 'stack_info', causing
unwind_dump() to start from the wrong address, flood the printk buffer,
and eventually read a bad address.

In other cases, dumping only the most recently accessed stack doesn't
give enough data to diagnose the error.

Fix both issues by dumping *all* stacks involved in the trace, not just
the last one.

Fixes: 8b5e99f02264 ("x86/unwind: Dump stack data on warnings")
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/unwind_frame.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index ae0821f..fec70fe 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -30,6 +30,8 @@ static void unwind_dump(struct unwind_state *state)
 	static bool dumped_before = false;
 	bool prev_zero, zero = false;
 	unsigned long word, *sp;
+	struct stack_info stack_info = {0};
+	unsigned long visit_mask = 0;
 
 	if (dumped_before)
 		return;
@@ -40,21 +42,27 @@ static void unwind_dump(struct unwind_state *state)
 			state->stack_info.type, state->stack_info.next_sp,
 			state->stack_mask, state->graph_idx);
 
-	for (sp = state->orig_sp; sp < state->stack_info.end; sp++) {
-		word = READ_ONCE_NOCHECK(*sp);
+	for (sp = state->orig_sp; sp; sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
+		if (get_stack_info(sp, state->task, &stack_info, &visit_mask))
+			break;
 
-		prev_zero = zero;
-		zero = word == 0;
+		for (; sp < stack_info.end; sp++) {
 
-		if (zero) {
-			if (!prev_zero)
-				printk_deferred("%p: %0*x ...\n",
-						sp, BITS_PER_LONG/4, 0);
-			continue;
-		}
+			word = READ_ONCE_NOCHECK(*sp);
+
+			prev_zero = zero;
+			zero = word == 0;
 
-		printk_deferred("%p: %0*lx (%pB)\n",
-				sp, BITS_PER_LONG/4, word, (void *)word);
+			if (zero) {
+				if (!prev_zero)
+					printk_deferred("%p: %0*x ...\n",
+							sp, BITS_PER_LONG/4, 0);
+				continue;
+			}
+
+			printk_deferred("%p: %0*lx (%pB)\n",
+					sp, BITS_PER_LONG/4, word, (void *)word);
+		}
 	}
 }
 
@@ -216,7 +224,7 @@ static bool update_stack_state(struct unwind_state *state,
 	}
 
 	/* Save the original stack pointer for unwind_dump(): */
-	if (!state->orig_sp || info->type != prev_type)
+	if (!state->orig_sp)
 		state->orig_sp = frame;
 
 	return true;
-- 
2.7.4