[PATCH AUTOSEL 4.14 14/39] x86/unwind/orc: Don't skip the first frame for inactive tasks

[Sasha Levin]

From: Miroslav Benes <mbenes@xxxxxxx>

[ Upstream commit f1d9a2abff66aa8156fbc1493abed468db63ea48 ]

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")
Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>
Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Dave Jones <dsj@xxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Link: https://lore.kernel.org/r/7f08db872ab59e807016910acdbe82f744de7065.1587808742.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 3bbb399f7ead3..8a855867e4568 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -574,7 +574,7 @@ 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;
-- 
2.20.1