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From: Jiri Slaby <jslaby@suse.cz>
To: tglx@linutronix.de
Cc: linux-kernel@vger.kernel.org, Jiri Slaby <jslaby@suse.cz>,
	Michal Suchanek <msuchanek@suse.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>
Subject: [PATCH v3] stacktrace: don't skip first entry on noncurrent tasks
Date: Wed, 30 Oct 2019 08:25:45 +0100
Message-ID: <20191030072545.19462-1-jslaby@suse.cz> (raw)
In-Reply-To: <20191029071944.17123-1-jslaby@suse.cz>

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.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Fixes: 214d8ca6ee85 ("stacktrace: Provide common infrastructure")
Tested-by: Michal Suchanek <msuchanek@suse.de>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---

Notes:
    [v2] add the same for the !ARCH_STACKWALK case
    
    [v3] fix build on !ARCH_STACKWALK

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

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 6d1f68b7e528..c9ea7eb2cb1a 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);
-- 
2.23.0


  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-25  6:52 [PATCH] " Jiri Slaby
2019-10-25 14:21 ` Josh Poimboeuf
2019-10-29  7:19   ` [PATCH v2] " Jiri Slaby
2019-10-29 13:35     ` Josh Poimboeuf
2019-10-30  6:09     ` Jiri Slaby
2019-10-30  7:25     ` Jiri Slaby [this message]
2019-11-04 20:24       ` [tip: core/urgent] stacktrace: Don't " tip-bot2 for Jiri Slaby

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