linux-kernel - [PATCH v2 08/11] x86/unwind/orc: Don't skip the first frame for inactive tasks

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Message-Id: <7f08db872ab59e807016910acdbe82f744de7065.1587808742.git.jpoimboe@redhat.com>
Date:   Sat, 25 Apr 2020 05:03:07 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Vince Weaver <vincent.weaver@...ne.edu>,
        Dave Jones <dsj@...com>, Jann Horn <jannh@...gle.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH v2 08/11] x86/unwind/orc: Don't skip the first frame for inactive tasks

From: Miroslav Benes <mbenes@...e.cz>

When unwinding an inactive task, the ORC unwinder skips the first frame
by default.  If both the 'regs' and 'first_frame' parameters of
unwind_start() are NULL, 'state->sp' and 'first_frame' are later
initialized to the same value for an inactive task.  Given there is a
"less than or equal to" comparison used at the end of __unwind_start()
for skipping stack frames, the first frame is skipped.

Drop the equal part of the comparison and make the behavior equivalent
to the frame pointer unwinder.

Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
Signed-off-by: Miroslav Benes <mbenes@...e.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Reviewed-by: Miroslav Benes <mbenes@...e.cz>
---
 arch/x86/kernel/unwind_orc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 45166fd50be3..e9f5a20c69c6 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -657,7 +657,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 	/* Otherwise, skip ahead to the user-specified starting frame: */
 	while (!unwind_done(state) &&
 	       (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
-			state->sp <= (unsigned long)first_frame))
+			state->sp < (unsigned long)first_frame))
 		unwind_next_frame(state);
 
 	return;
-- 
2.21.1