[PATCH] stacktrace: don't skip first entry on noncurrent tasks

[PATCH] stacktrace: don't skip first entry on noncurrent tasks

[Jiri Slaby]

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")
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
---
 kernel/stacktrace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 6d1f68b7e528..d06a2e4d0142 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))
-- 
2.23.0

Re: [PATCH] stacktrace: don't skip first entry on noncurrent tasks

[Josh Poimboeuf]

On Fri, Oct 25, 2019 at 08:52:26AM +0200, Jiri Slaby wrote:
> 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")
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
>  kernel/stacktrace.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
> index 6d1f68b7e528..d06a2e4d0142 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))

I think a similar change is needed for the other !CONFIG_ARCH_STACKWALK
version of stack_trace_save_tsk() in that file?

-- 
Josh

[PATCH v2] stacktrace: don't skip first entry on noncurrent tasks

[Jiri Slaby]

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")
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
---

Notes:
    [v2] add the same for the !CONFIG_ARCH_STACKWALK case

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

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 6d1f68b7e528..48703b252434 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 == tsk),
 	};
 
 	save_stack_trace_tsk(task, &trace);
-- 
2.23.0

Re: [PATCH v2] stacktrace: don't skip first entry on noncurrent tasks

[Josh Poimboeuf]

On Tue, Oct 29, 2019 at 08:19:44AM +0100, Jiri Slaby wrote:
> 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")
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
> 
> Notes:
>     [v2] add the same for the !CONFIG_ARCH_STACKWALK case

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

-- 
Josh

Re: [PATCH v2] stacktrace: don't skip first entry on noncurrent tasks

[Jiri Slaby]

On 29. 10. 19, 8:19, Jiri Slaby wrote:
> --- a/kernel/stacktrace.c
> +++ b/kernel/stacktrace.c
> @@ -298,7 +299,8 @@ unsigned int stack_trace_save_tsk(struct task_struct *task,

Argh, "task" here and:

>  	struct stack_trace trace = {
>  		.entries	= store,
>  		.max_entries	= size,
> -		.skip		= skipnr + 1,
> +		/* skip this function if they are tracing us */
> +		.skip	= skipnr + !!(current == tsk),

"tsk" here. Scratch this one.

thanks,
-- 
js
suse labs

[PATCH v3] stacktrace: don't skip first entry on noncurrent tasks

[Jiri Slaby]

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

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

[tip-bot2 for Jiri Slaby]

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@suse.cz>
AuthorDate:    Wed, 30 Oct 2019 08:25:45 +01:00
Committer:     Thomas Gleixner <tglx@linutronix.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@suse.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michal Suchanek <msuchanek@suse.de>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.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);