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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@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);
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