Commit b3b9cb11 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt (Google)
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unwind: Finish up unwind when a task exits 

On do_exit() when a task is exiting, if a unwind is requested and the
deferred user stacktrace is deferred via the task_work, the task_work
callback is called after exit_mm() is called in do_exit(). This means that
the user stack trace will not be retrieved and an empty stack is created.

Instead, add a function unwind_deferred_task_exit() and call it just
before exit_mm() so that the unwinder can call the requested callbacks
with the user space stack.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Jens Remus <jremus@linux.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182406.504259474@kernel.org


Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 357eda2d

include/linux/unwind_deferred.h

+3 −0
Original line number Diff line number Diff line
@@ -39,6 +39,8 @@ int unwind_deferred_init(struct unwind_work *work, unwind_callback_t func); 
int unwind_deferred_request(struct unwind_work *work, u64 *cookie);

void unwind_deferred_cancel(struct unwind_work *work);



void unwind_deferred_task_exit(struct task_struct *task);



static __always_inline void unwind_reset_info(void)

{

	struct unwind_task_info *info = &current->unwind_info;
@@ -71,6 +73,7 @@ static inline int unwind_deferred_init(struct unwind_work *work, unwind_callback 
static inline int unwind_deferred_request(struct unwind_work *work, u64 *timestamp) { return -ENOSYS; }

static inline void unwind_deferred_cancel(struct unwind_work *work) {}



static inline void unwind_deferred_task_exit(struct task_struct *task) {}

static inline void unwind_reset_info(void) {}



#endif /* !CONFIG_UNWIND_USER */

kernel/exit.c

+2 −0
Original line number Diff line number Diff line
@@ -68,6 +68,7 @@ 
#include <linux/rethook.h>

#include <linux/sysfs.h>

#include <linux/user_events.h>

#include <linux/unwind_deferred.h>

#include <linux/uaccess.h>

#include <linux/pidfs.h>
@@ -938,6 +939,7 @@ void __noreturn do_exit(long code) 


	tsk->exit_code = code;

	taskstats_exit(tsk, group_dead);

	unwind_deferred_task_exit(tsk);

	trace_sched_process_exit(tsk, group_dead);



	/*

kernel/unwind/deferred.c

+20 −3
Original line number Diff line number Diff line
@@ -114,7 +114,7 @@ int unwind_user_faultable(struct unwind_stacktrace *trace) 
	/* Should always be called from faultable context */

	might_fault();



	if (current->flags & PF_EXITING)

	if (!current->mm)

		return -EINVAL;



	if (!info->cache) {
@@ -147,9 +147,9 @@ int unwind_user_faultable(struct unwind_stacktrace *trace) 
	return 0;

}



static void unwind_deferred_task_work(struct callback_head *head)

static void process_unwind_deferred(struct task_struct *task)

{

	struct unwind_task_info *info = container_of(head, struct unwind_task_info, work);

	struct unwind_task_info *info = &task->unwind_info;

	struct unwind_stacktrace trace;

	struct unwind_work *work;

	unsigned long bits;
@@ -186,6 +186,23 @@ static void unwind_deferred_task_work(struct callback_head *head) 
	}

}



static void unwind_deferred_task_work(struct callback_head *head)

{

	process_unwind_deferred(current);

}



void unwind_deferred_task_exit(struct task_struct *task)

{

	struct unwind_task_info *info = &current->unwind_info;



	if (!unwind_pending(info))

		return;



	process_unwind_deferred(task);



	task_work_cancel(task, &info->work);

}



/**

 * unwind_deferred_request - Request a user stacktrace on task kernel exit

 * @work: Unwind descriptor requesting the trace