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: Steven Rostedt (Google) <rostedt@goodmis.org>
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@ -39,6 +39,8 @@ int unwind_deferred_init(struct unwind_work *work, unwind_callback_t func);
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int unwind_deferred_request(struct unwind_work *work, u64 *cookie);
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void unwind_deferred_cancel(struct unwind_work *work);
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void unwind_deferred_task_exit(struct task_struct *task);
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static __always_inline void unwind_reset_info(void)
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{
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struct unwind_task_info *info = ¤t->unwind_info;
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@ -71,6 +73,7 @@ static inline int unwind_deferred_init(struct unwind_work *work, unwind_callback
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static inline int unwind_deferred_request(struct unwind_work *work, u64 *timestamp) { return -ENOSYS; }
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static inline void unwind_deferred_cancel(struct unwind_work *work) {}
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static inline void unwind_deferred_task_exit(struct task_struct *task) {}
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static inline void unwind_reset_info(void) {}
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#endif /* !CONFIG_UNWIND_USER */
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@ -68,6 +68,7 @@
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#include <linux/rethook.h>
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#include <linux/sysfs.h>
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#include <linux/user_events.h>
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#include <linux/unwind_deferred.h>
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#include <linux/uaccess.h>
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#include <linux/pidfs.h>
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@ -938,6 +939,7 @@ void __noreturn do_exit(long code)
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tsk->exit_code = code;
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taskstats_exit(tsk, group_dead);
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unwind_deferred_task_exit(tsk);
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trace_sched_process_exit(tsk, group_dead);
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/*
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@ -114,7 +114,7 @@ int unwind_user_faultable(struct unwind_stacktrace *trace)
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/* Should always be called from faultable context */
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might_fault();
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if (current->flags & PF_EXITING)
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if (!current->mm)
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return -EINVAL;
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if (!info->cache) {
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@ -147,9 +147,9 @@ int unwind_user_faultable(struct unwind_stacktrace *trace)
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return 0;
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}
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static void unwind_deferred_task_work(struct callback_head *head)
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static void process_unwind_deferred(struct task_struct *task)
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{
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struct unwind_task_info *info = container_of(head, struct unwind_task_info, work);
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struct unwind_task_info *info = &task->unwind_info;
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struct unwind_stacktrace trace;
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struct unwind_work *work;
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unsigned long bits;
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@ -186,6 +186,23 @@ static void unwind_deferred_task_work(struct callback_head *head)
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}
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}
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static void unwind_deferred_task_work(struct callback_head *head)
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{
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process_unwind_deferred(current);
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}
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void unwind_deferred_task_exit(struct task_struct *task)
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{
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struct unwind_task_info *info = ¤t->unwind_info;
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if (!unwind_pending(info))
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return;
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process_unwind_deferred(task);
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task_work_cancel(task, &info->work);
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}
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/**
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* unwind_deferred_request - Request a user stacktrace on task kernel exit
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* @work: Unwind descriptor requesting the trace
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