linux-kernel - [tip: core/urgent] stacktrace: Don't skip first entry on noncurrent tasks

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Message-ID: <157289904416.29376.6390821004707816453.tip-bot2@tip-bot2>
Date:   Mon, 04 Nov 2019 20:24:04 -0000
From:   "tip-bot2 for Jiri Slaby" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Jiri Slaby <jslaby@...e.cz>, Thomas Gleixner <tglx@...utronix.de>,
        Michal Suchanek <msuchanek@...e.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        linux-kernel@...r.kernel.org
Subject: [tip: core/urgent] stacktrace: Don't skip first entry on noncurrent tasks

The following commit has been merged into the core/urgent branch of tip:

Commit-ID:     b0c51f158455e31d5024100cf3580fcd88214b0e
Gitweb:        https://git.kernel.org/tip/b0c51f158455e31d5024100cf3580fcd88214b0e
Author:        Jiri Slaby <jslaby@...e.cz>
AuthorDate:    Wed, 30 Oct 2019 08:25:45 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Mon, 04 Nov 2019 21:19:25 +01:00

stacktrace: Don't skip first entry on noncurrent tasks

When doing cat /proc/<PID>/stack, the output is missing the first entry.
When the current code walks the stack starting in stack_trace_save_tsk,
it skips all scheduler functions (that's OK) plus one more function. But
this one function should be skipped only for the 'current' task as it is
stack_trace_save_tsk proper.

The original code (before the common infrastructure) skipped one
function only for the 'current' task -- see save_stack_trace_tsk before
3599fe12a125. So do so also in the new infrastructure now.

Fixes: 214d8ca6ee85 ("stacktrace: Provide common infrastructure")
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Michal Suchanek <msuchanek@...e.de>
Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
Link: https://lkml.kernel.org/r/20191030072545.19462-1-jslaby@suse.cz

---
 kernel/stacktrace.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 6d1f68b..c9ea7eb 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -141,7 +141,8 @@ unsigned int stack_trace_save_tsk(struct task_struct *tsk, unsigned long *store,
 	struct stacktrace_cookie c = {
 		.store	= store,
 		.size	= size,
-		.skip	= skipnr + 1,
+		/* skip this function if they are tracing us */
+		.skip	= skipnr + !!(current == tsk),
 	};
 
 	if (!try_get_task_stack(tsk))
@@ -298,7 +299,8 @@ unsigned int stack_trace_save_tsk(struct task_struct *task,
 	struct stack_trace trace = {
 		.entries	= store,
 		.max_entries	= size,
-		.skip		= skipnr + 1,
+		/* skip this function if they are tracing us */
+		.skip	= skipnr + !!(current == task),
 	};
 
 	save_stack_trace_tsk(task, &trace);