Commit 5e32d0f1 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt (Google)
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unwind_user/deferred: Add unwind_user_faultable() 

Add a new API to retrieve a user space callstack called
unwind_user_faultable(). The difference between this user space stack
tracer from the current user space stack tracer is that this must be
called from faultable context as it may use routines to access user space
data that needs to be faulted in.

It can be safely called from entering or exiting a system call as the code
can still be faulted in there.

This code is based on work by Josh Poimboeuf's deferred unwinding code:

Link: https://lore.kernel.org/all/6052e8487746603bdb29b65f4033e739092d9925.1737511963.git.jpoimboe@kernel.org/

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: 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/20250729182405.147896868@kernel.org


Reviewed-by: default avatarJens Remus <jremus@linux.ibm.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 71753c6e

include/linux/sched.h

+5 −0
Original line number Diff line number Diff line
@@ -46,6 +46,7 @@ 
#include <linux/rv.h>

#include <linux/uidgid_types.h>

#include <linux/tracepoint-defs.h>

#include <linux/unwind_deferred_types.h>

#include <asm/kmap_size.h>



/* task_struct member predeclarations (sorted alphabetically): */
@@ -1654,6 +1655,10 @@ struct task_struct { 
	struct user_event_mm		*user_event_mm;

#endif



#ifdef CONFIG_UNWIND_USER

	struct unwind_task_info		unwind_info;

#endif



	/* CPU-specific state of this task: */

	struct thread_struct		thread;

include/linux/unwind_deferred.h

0 → 100644
+24 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef _LINUX_UNWIND_USER_DEFERRED_H

#define _LINUX_UNWIND_USER_DEFERRED_H



#include <linux/unwind_user.h>

#include <linux/unwind_deferred_types.h>



#ifdef CONFIG_UNWIND_USER



void unwind_task_init(struct task_struct *task);

void unwind_task_free(struct task_struct *task);



int unwind_user_faultable(struct unwind_stacktrace *trace);



#else /* !CONFIG_UNWIND_USER */



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

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



static inline int unwind_user_faultable(struct unwind_stacktrace *trace) { return -ENOSYS; }



#endif /* !CONFIG_UNWIND_USER */



#endif /* _LINUX_UNWIND_USER_DEFERRED_H */

include/linux/unwind_deferred_types.h

0 → 100644
+9 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef _LINUX_UNWIND_USER_DEFERRED_TYPES_H

#define _LINUX_UNWIND_USER_DEFERRED_TYPES_H



struct unwind_task_info {

	unsigned long		*entries;

};



#endif /* _LINUX_UNWIND_USER_DEFERRED_TYPES_H */

kernel/fork.c

+4 −0
Original line number Diff line number Diff line
@@ -105,6 +105,7 @@ 
#include <uapi/linux/pidfd.h>

#include <linux/pidfs.h>

#include <linux/tick.h>

#include <linux/unwind_deferred.h>



#include <asm/pgalloc.h>

#include <linux/uaccess.h>
@@ -732,6 +733,7 @@ void __put_task_struct(struct task_struct *tsk) 
	WARN_ON(refcount_read(&tsk->usage));

	WARN_ON(tsk == current);



	unwind_task_free(tsk);

	sched_ext_free(tsk);

	io_uring_free(tsk);

	cgroup_free(tsk);
@@ -2135,6 +2137,8 @@ __latent_entropy struct task_struct *copy_process( 
	p->bpf_ctx = NULL;

#endif



	unwind_task_init(p);



	/* Perform scheduler related setup. Assign this task to a CPU. */

	retval = sched_fork(clone_flags, p);

	if (retval)

kernel/unwind/Makefile

+1 −1
Original line number Diff line number Diff line 
 obj-$(CONFIG_UNWIND_USER) += user.o
 
 obj-$(CONFIG_UNWIND_USER)	+= user.o deferred.o