Re: [PATCH v2 2/6] sched: Add wrapper for get_wchan() to keep task blocked

From: Peter Zijlstra
Date: Thu Sep 30 2021 - 04:28:38 EST

On Wed, Sep 29, 2021 at 03:02:14PM -0700, Kees Cook wrote:
> Having a stable wchan means the process must be blocked and for it to
> stay that way while performing stack unwinding.

How's this instead?

---
Subject: sched: Wrap get_wchan() to keep task blocked
From: Kees Cook <keescook@xxxxxxxxxxxx>
Date: Wed, 29 Sep 2021 15:02:14 -0700

From: Kees Cook <keescook@xxxxxxxxxxxx>

Having a stable wchan means the process must be blocked and for it to
stay that way while performing stack unwinding.

Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
[peterz: __get_wchan]
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/alpha/include/asm/processor.h | 2 +-
arch/alpha/kernel/process.c | 5 ++---
arch/arc/include/asm/processor.h | 2 +-
arch/arc/kernel/stacktrace.c | 4 ++--
arch/arm/include/asm/processor.h | 2 +-
arch/arm/kernel/process.c | 4 +---
arch/arm64/include/asm/processor.h | 2 +-
arch/arm64/kernel/process.c | 4 +---
arch/csky/include/asm/processor.h | 2 +-
arch/csky/kernel/stacktrace.c | 5 ++---
arch/h8300/include/asm/processor.h | 2 +-
arch/h8300/kernel/process.c | 5 +----
arch/hexagon/include/asm/processor.h | 2 +-
arch/hexagon/kernel/process.c | 4 +---
arch/ia64/include/asm/processor.h | 2 +-
arch/ia64/kernel/process.c | 5 +----
arch/m68k/include/asm/processor.h | 2 +-
arch/m68k/kernel/process.c | 4 +---
arch/microblaze/include/asm/processor.h | 2 +-
arch/microblaze/kernel/process.c | 2 +-
arch/mips/include/asm/processor.h | 2 +-
arch/mips/kernel/process.c | 8 +++-----
arch/nds32/include/asm/processor.h | 2 +-
arch/nds32/kernel/process.c | 7 +------
arch/nios2/include/asm/processor.h | 2 +-
arch/nios2/kernel/process.c | 5 +----
arch/openrisc/include/asm/processor.h | 2 +-
arch/openrisc/kernel/process.c | 2 +-
arch/parisc/include/asm/processor.h | 2 +-
arch/parisc/kernel/process.c | 5 +----
arch/powerpc/include/asm/processor.h | 2 +-
arch/powerpc/kernel/process.c | 9 +++------
arch/riscv/include/asm/processor.h | 2 +-
arch/riscv/kernel/stacktrace.c | 12 +++++-------
arch/s390/include/asm/processor.h | 2 +-
arch/s390/kernel/process.c | 4 ++--
arch/sh/include/asm/processor_32.h | 2 +-
arch/sh/kernel/process_32.c | 5 +----
arch/sparc/include/asm/processor_32.h | 2 +-
arch/sparc/include/asm/processor_64.h | 2 +-
arch/sparc/kernel/process_32.c | 5 +----
arch/sparc/kernel/process_64.c | 5 +----
arch/um/include/asm/processor-generic.h | 2 +-
arch/um/kernel/process.c | 5 +----
arch/x86/include/asm/processor.h | 2 +-
arch/x86/kernel/process.c | 5 +----
arch/xtensa/include/asm/processor.h | 2 +-
arch/xtensa/kernel/process.c | 5 +----
include/linux/sched.h | 1 +
kernel/sched/core.c | 19 +++++++++++++++++++
50 files changed, 80 insertions(+), 112 deletions(-)

--- a/arch/alpha/include/asm/processor.h
+++ b/arch/alpha/include/asm/processor.h
@@ -42,7 +42,7 @@ extern void start_thread(struct pt_regs
struct task_struct;
extern void release_thread(struct task_struct *);

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

#define KSTK_EIP(tsk) (task_pt_regs(tsk)->pc)

--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -376,12 +376,11 @@ thread_saved_pc(struct task_struct *t)
}

unsigned long
-get_wchan(struct task_struct *p)
+__get_wchan(struct task_struct *p)
{
unsigned long schedule_frame;
unsigned long pc;
- if (!p || p == current || task_is_running(p))
- return 0;
+
/*
* This one depends on the frame size of schedule(). Do a
* "disass schedule" in gdb to find the frame size. Also, the
--- a/arch/arc/include/asm/processor.h
+++ b/arch/arc/include/asm/processor.h
@@ -70,7 +70,7 @@ struct task_struct;
extern void start_thread(struct pt_regs * regs, unsigned long pc,
unsigned long usp);

-extern unsigned int get_wchan(struct task_struct *p);
+extern unsigned int __get_wchan(struct task_struct *p);

#endif /* !__ASSEMBLY__ */

--- a/arch/arc/kernel/stacktrace.c
+++ b/arch/arc/kernel/stacktrace.c
@@ -15,7 +15,7 @@
* = specifics of data structs where trace is saved(CONFIG_STACKTRACE etc)
*
* vineetg: March 2009
- * -Implemented correct versions of thread_saved_pc() and get_wchan()
+ * -Implemented correct versions of thread_saved_pc() and __get_wchan()
*
* rajeshwarr: 2008
* -Initial implementation
@@ -248,7 +248,7 @@ void show_stack(struct task_struct *tsk,
* Of course just returning schedule( ) would be pointless so unwind until
* the function is not in schedular code
*/
-unsigned int get_wchan(struct task_struct *tsk)
+unsigned int __get_wchan(struct task_struct *tsk)
{
return arc_unwind_core(tsk, NULL, __get_first_nonsched, NULL);
}
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -84,7 +84,7 @@ struct task_struct;
/* Free all resources held by a thread. */
extern void release_thread(struct task_struct *);

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

#define task_pt_regs(p) \
((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1)
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -276,13 +276,11 @@ int copy_thread(unsigned long clone_flag
return 0;
}

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
struct stackframe frame;
unsigned long stack_page;
int count = 0;
- if (!p || p == current || task_is_running(p))
- return 0;

frame.fp = thread_saved_fp(p);
frame.sp = thread_saved_sp(p);
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -257,7 +257,7 @@ struct task_struct;
/* Free all resources held by a thread. */
extern void release_thread(struct task_struct *);

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

void update_sctlr_el1(u64 sctlr);

--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -528,13 +528,11 @@ __notrace_funcgraph struct task_struct *
return last;
}

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
struct stackframe frame;
unsigned long stack_page, ret = 0;
int count = 0;
- if (!p || p == current || task_is_running(p))
- return 0;

stack_page = (unsigned long)try_get_task_stack(p);
if (!stack_page)
--- a/arch/csky/include/asm/processor.h
+++ b/arch/csky/include/asm/processor.h
@@ -81,7 +81,7 @@ static inline void release_thread(struct

extern int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

#define KSTK_EIP(tsk) (task_pt_regs(tsk)->pc)
#define KSTK_ESP(tsk) (task_pt_regs(tsk)->usp)
--- a/arch/csky/kernel/stacktrace.c
+++ b/arch/csky/kernel/stacktrace.c
@@ -111,12 +111,11 @@ static bool save_wchan(unsigned long pc,
return false;
}

-unsigned long get_wchan(struct task_struct *task)
+unsigned long __get_wchan(struct task_struct *task)
{
unsigned long pc = 0;

- if (likely(task && task != current && !task_is_running(task)))
- walk_stackframe(task, NULL, save_wchan, &pc);
+ walk_stackframe(task, NULL, save_wchan, &pc);
return pc;
}

--- a/arch/h8300/include/asm/processor.h
+++ b/arch/h8300/include/asm/processor.h
@@ -105,7 +105,7 @@ static inline void release_thread(struct
{
}

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

#define KSTK_EIP(tsk) \
({ \
--- a/arch/h8300/kernel/process.c
+++ b/arch/h8300/kernel/process.c
@@ -128,15 +128,12 @@ int copy_thread(unsigned long clone_flag
return 0;
}

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long fp, pc;
unsigned long stack_page;
int count = 0;

- if (!p || p == current || task_is_running(p))
- return 0;
-
stack_page = (unsigned long)p;
fp = ((struct pt_regs *)p->thread.ksp)->er6;
do {
--- a/arch/hexagon/include/asm/processor.h
+++ b/arch/hexagon/include/asm/processor.h
@@ -64,7 +64,7 @@ struct thread_struct {
extern void release_thread(struct task_struct *dead_task);

/* Get wait channel for task P. */
-extern unsigned long get_wchan(struct task_struct *p);
+extern unsigned long __get_wchan(struct task_struct *p);

/* The following stuff is pretty HEXAGON specific. */

--- a/arch/hexagon/kernel/process.c
+++ b/arch/hexagon/kernel/process.c
@@ -130,13 +130,11 @@ void flush_thread(void)
* is an identification of the point at which the scheduler
* was invoked by a blocked thread.
*/
-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long fp, pc;
unsigned long stack_page;
int count = 0;
- if (!p || p == current || task_is_running(p))
- return 0;

stack_page = (unsigned long)task_stack_page(p);
fp = ((struct hexagon_switch_stack *)p->thread.switch_sp)->fp;
--- a/arch/ia64/include/asm/processor.h
+++ b/arch/ia64/include/asm/processor.h
@@ -330,7 +330,7 @@ struct task_struct;
#define release_thread(dead_task)

/* Get wait channel for task P. */
-extern unsigned long get_wchan (struct task_struct *p);
+extern unsigned long __get_wchan (struct task_struct *p);

/* Return instruction pointer of blocked task TSK. */
#define KSTK_EIP(tsk) \
--- a/arch/ia64/kernel/process.c
+++ b/arch/ia64/kernel/process.c
@@ -523,15 +523,12 @@ exit_thread (struct task_struct *tsk)
}

unsigned long
-get_wchan (struct task_struct *p)
+__get_wchan (struct task_struct *p)
{
struct unw_frame_info info;
unsigned long ip;
int count = 0;

- if (!p || p == current || task_is_running(p))
- return 0;
-
/*
* Note: p may not be a blocked task (it could be current or
* another process running on some other CPU. Rather than
--- a/arch/m68k/include/asm/processor.h
+++ b/arch/m68k/include/asm/processor.h
@@ -125,7 +125,7 @@ static inline void release_thread(struct
{
}

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

#define KSTK_EIP(tsk) \
({ \
--- a/arch/m68k/kernel/process.c
+++ b/arch/m68k/kernel/process.c
@@ -263,13 +263,11 @@ int dump_fpu (struct pt_regs *regs, stru
}
EXPORT_SYMBOL(dump_fpu);

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long fp, pc;
unsigned long stack_page;
int count = 0;
- if (!p || p == current || task_is_running(p))
- return 0;

stack_page = (unsigned long)task_stack_page(p);
fp = ((struct switch_stack *)p->thread.ksp)->a6;
--- a/arch/microblaze/include/asm/processor.h
+++ b/arch/microblaze/include/asm/processor.h
@@ -68,7 +68,7 @@ static inline void release_thread(struct
{
}

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

/* The size allocated for kernel stacks. This _must_ be a power of two! */
# define KERNEL_STACK_SIZE 0x2000
--- a/arch/microblaze/kernel/process.c
+++ b/arch/microblaze/kernel/process.c
@@ -112,7 +112,7 @@ int copy_thread(unsigned long clone_flag
return 0;
}

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
/* TBD (used by procfs) */
return 0;
--- a/arch/mips/include/asm/processor.h
+++ b/arch/mips/include/asm/processor.h
@@ -369,7 +369,7 @@ static inline void flush_thread(void)
{
}

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

#define __KSTK_TOS(tsk) ((unsigned long)task_stack_page(tsk) + \
THREAD_SIZE - 32 - sizeof(struct pt_regs))
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -511,7 +511,7 @@ static int __init frame_info_init(void)

/*
* Without schedule() frame info, result given by
- * thread_saved_pc() and get_wchan() are not reliable.
+ * thread_saved_pc() and __get_wchan() are not reliable.
*/
if (schedule_mfi.pc_offset < 0)
printk("Can't analyze schedule() prologue at %p\n", schedule);
@@ -652,9 +652,9 @@ unsigned long unwind_stack(struct task_s
#endif

/*
- * get_wchan - a maintenance nightmare^W^Wpain in the ass ...
+ * __get_wchan - a maintenance nightmare^W^Wpain in the ass ...
*/
-unsigned long get_wchan(struct task_struct *task)
+unsigned long __get_wchan(struct task_struct *task)
{
unsigned long pc = 0;
#ifdef CONFIG_KALLSYMS
@@ -662,8 +662,6 @@ unsigned long get_wchan(struct task_stru
unsigned long ra = 0;
#endif

- if (!task || task == current || task_is_running(task))
- goto out;
if (!task_stack_page(task))
goto out;

--- a/arch/nds32/include/asm/processor.h
+++ b/arch/nds32/include/asm/processor.h
@@ -83,7 +83,7 @@ extern struct task_struct *last_task_use
/* Prepare to copy thread state - unlazy all lazy status */
#define prepare_to_copy(tsk) do { } while (0)

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

#define cpu_relax() barrier()

--- a/arch/nds32/kernel/process.c
+++ b/arch/nds32/kernel/process.c
@@ -233,15 +233,12 @@ int dump_fpu(struct pt_regs *regs, elf_f

EXPORT_SYMBOL(dump_fpu);

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long fp, lr;
unsigned long stack_start, stack_end;
int count = 0;

- if (!p || p == current || task_is_running(p))
- return 0;
-
if (IS_ENABLED(CONFIG_FRAME_POINTER)) {
stack_start = (unsigned long)end_of_stack(p);
stack_end = (unsigned long)task_stack_page(p) + THREAD_SIZE;
@@ -258,5 +255,3 @@ unsigned long get_wchan(struct task_stru
}
return 0;
}
-
-EXPORT_SYMBOL(get_wchan);
--- a/arch/nios2/include/asm/processor.h
+++ b/arch/nios2/include/asm/processor.h
@@ -69,7 +69,7 @@ static inline void release_thread(struct
{
}

-extern unsigned long get_wchan(struct task_struct *p);
+extern unsigned long __get_wchan(struct task_struct *p);

#define task_pt_regs(p) \
((struct pt_regs *)(THREAD_SIZE + task_stack_page(p)) - 1)
--- a/arch/nios2/kernel/process.c
+++ b/arch/nios2/kernel/process.c
@@ -217,15 +217,12 @@ void dump(struct pt_regs *fp)
pr_emerg("\n\n");
}

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long fp, pc;
unsigned long stack_page;
int count = 0;

- if (!p || p == current || task_is_running(p))
- return 0;
-
stack_page = (unsigned long)p;
fp = ((struct switch_stack *)p->thread.ksp)->fp; /* ;dgt2 */
do {
--- a/arch/openrisc/include/asm/processor.h
+++ b/arch/openrisc/include/asm/processor.h
@@ -73,7 +73,7 @@ struct thread_struct {

void start_thread(struct pt_regs *regs, unsigned long nip, unsigned long sp);
void release_thread(struct task_struct *);
-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

#define cpu_relax() barrier()

--- a/arch/openrisc/kernel/process.c
+++ b/arch/openrisc/kernel/process.c
@@ -263,7 +263,7 @@ void dump_elf_thread(elf_greg_t *dest, s
dest[35] = 0;
}

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
/* TODO */

--- a/arch/parisc/include/asm/processor.h
+++ b/arch/parisc/include/asm/processor.h
@@ -273,7 +273,7 @@ struct mm_struct;
/* Free all resources held by a thread. */
extern void release_thread(struct task_struct *);

-extern unsigned long get_wchan(struct task_struct *p);
+extern unsigned long __get_wchan(struct task_struct *p);

#define KSTK_EIP(tsk) ((tsk)->thread.regs.iaoq[0])
#define KSTK_ESP(tsk) ((tsk)->thread.regs.gr[30])
--- a/arch/parisc/kernel/process.c
+++ b/arch/parisc/kernel/process.c
@@ -240,15 +240,12 @@ copy_thread(unsigned long clone_flags, u
}

unsigned long
-get_wchan(struct task_struct *p)
+__get_wchan(struct task_struct *p)
{
struct unwind_frame_info info;
unsigned long ip;
int count = 0;

- if (!p || p == current || task_is_running(p))
- return 0;
-
/*
* These bracket the sleeping functions..
*/
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -300,7 +300,7 @@ struct thread_struct {

#define task_pt_regs(tsk) ((tsk)->thread.regs)

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

#define KSTK_EIP(tsk) ((tsk)->thread.regs? (tsk)->thread.regs->nip: 0)
#define KSTK_ESP(tsk) ((tsk)->thread.regs? (tsk)->thread.regs->gpr[1]: 0)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2111,14 +2111,11 @@ int validate_sp(unsigned long sp, struct

EXPORT_SYMBOL(validate_sp);

-static unsigned long __get_wchan(struct task_struct *p)
+static unsigned long ___get_wchan(struct task_struct *p)
{
unsigned long ip, sp;
int count = 0;

- if (!p || p == current || task_is_running(p))
- return 0;
-
sp = p->thread.ksp;
if (!validate_sp(sp, p, STACK_FRAME_OVERHEAD))
return 0;
@@ -2137,14 +2134,14 @@ static unsigned long __get_wchan(struct
return 0;
}

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long ret;

if (!try_get_task_stack(p))
return 0;

- ret = __get_wchan(p);
+ ret = ___get_wchan(p);

put_task_stack(p);

--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -66,7 +66,7 @@ static inline void release_thread(struct
{
}

-extern unsigned long get_wchan(struct task_struct *p);
+extern unsigned long __get_wchan(struct task_struct *p);


static inline void wait_for_interrupt(void)
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -128,16 +128,14 @@ static bool save_wchan(void *arg, unsign
return true;
}

-unsigned long get_wchan(struct task_struct *task)
+unsigned long __get_wchan(struct task_struct *task)
{
unsigned long pc = 0;

- if (likely(task && task != current && !task_is_running(task))) {
- if (!try_get_task_stack(task))
- return 0;
- walk_stackframe(task, NULL, save_wchan, &pc);
- put_task_stack(task);
- }
+ if (!try_get_task_stack(task))
+ return 0;
+ walk_stackframe(task, NULL, save_wchan, &pc);
+ put_task_stack(task);
return pc;
}

--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -192,7 +192,7 @@ static inline void release_thread(struct
void guarded_storage_release(struct task_struct *tsk);
void gs_load_bc_cb(struct pt_regs *regs);

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);
#define task_pt_regs(tsk) ((struct pt_regs *) \
(task_stack_page(tsk) + THREAD_SIZE) - 1)
#define KSTK_EIP(tsk) (task_pt_regs(tsk)->psw.addr)
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -181,12 +181,12 @@ void execve_tail(void)
asm volatile("sfpc %0" : : "d" (0));
}

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
struct unwind_state state;
unsigned long ip = 0;

- if (!p || p == current || task_is_running(p) || !task_stack_page(p))
+ if (!task_stack_page(p))
return 0;

if (!try_get_task_stack(p))
--- a/arch/sh/include/asm/processor_32.h
+++ b/arch/sh/include/asm/processor_32.h
@@ -180,7 +180,7 @@ static inline void show_code(struct pt_r
}
#endif

-extern unsigned long get_wchan(struct task_struct *p);
+extern unsigned long __get_wchan(struct task_struct *p);

#define KSTK_EIP(tsk) (task_pt_regs(tsk)->pc)
#define KSTK_ESP(tsk) (task_pt_regs(tsk)->regs[15])
--- a/arch/sh/kernel/process_32.c
+++ b/arch/sh/kernel/process_32.c
@@ -182,13 +182,10 @@ __switch_to(struct task_struct *prev, st
return prev;
}

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long pc;

- if (!p || p == current || task_is_running(p))
- return 0;
-
/*
* The same comment as on the Alpha applies here, too ...
*/
--- a/arch/sparc/include/asm/processor_32.h
+++ b/arch/sparc/include/asm/processor_32.h
@@ -89,7 +89,7 @@ static inline void start_thread(struct p
/* Free all resources held by a thread. */
#define release_thread(tsk) do { } while(0)

-unsigned long get_wchan(struct task_struct *);
+unsigned long __get_wchan(struct task_struct *);

#define task_pt_regs(tsk) ((tsk)->thread.kregs)
#define KSTK_EIP(tsk) ((tsk)->thread.kregs->pc)
--- a/arch/sparc/include/asm/processor_64.h
+++ b/arch/sparc/include/asm/processor_64.h
@@ -183,7 +183,7 @@ do { \
/* Free all resources held by a thread. */
#define release_thread(tsk) do { } while (0)

-unsigned long get_wchan(struct task_struct *task);
+unsigned long __get_wchan(struct task_struct *task);

#define task_pt_regs(tsk) (task_thread_info(tsk)->kregs)
#define KSTK_EIP(tsk) (task_pt_regs(tsk)->tpc)
--- a/arch/sparc/kernel/process_32.c
+++ b/arch/sparc/kernel/process_32.c
@@ -365,7 +365,7 @@ int copy_thread(unsigned long clone_flag
return 0;
}

-unsigned long get_wchan(struct task_struct *task)
+unsigned long __get_wchan(struct task_struct *task)
{
unsigned long pc, fp, bias = 0;
unsigned long task_base = (unsigned long) task;
@@ -373,9 +373,6 @@ unsigned long get_wchan(struct task_stru
struct reg_window32 *rw;
int count = 0;

- if (!task || task == current || task_is_running(task))
- goto out;
-
fp = task_thread_info(task)->ksp + bias;
do {
/* Bogus frame pointer? */
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -663,7 +663,7 @@ int arch_dup_task_struct(struct task_str
return 0;
}

-unsigned long get_wchan(struct task_struct *task)
+unsigned long __get_wchan(struct task_struct *task)
{
unsigned long pc, fp, bias = 0;
struct thread_info *tp;
@@ -671,9 +671,6 @@ unsigned long get_wchan(struct task_stru
unsigned long ret = 0;
int count = 0;

- if (!task || task == current || task_is_running(task))
- goto out;
-
tp = task_thread_info(task);
bias = STACK_BIAS;
fp = task_thread_info(task)->ksp + bias;
--- a/arch/um/include/asm/processor-generic.h
+++ b/arch/um/include/asm/processor-generic.h
@@ -106,6 +106,6 @@ extern struct cpuinfo_um boot_cpu_data;
#define cache_line_size() (boot_cpu_data.cache_alignment)

#define KSTK_REG(tsk, reg) get_thread_reg(reg, &tsk->thread.switch_buf)
-extern unsigned long get_wchan(struct task_struct *p);
+extern unsigned long __get_wchan(struct task_struct *p);

#endif
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -364,14 +364,11 @@ unsigned long arch_align_stack(unsigned
}
#endif

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long stack_page, sp, ip;
bool seen_sched = 0;

- if ((p == NULL) || (p == current) || task_is_running(p))
- return 0;
-
stack_page = (unsigned long) task_stack_page(p);
/* Bail if the process has no kernel stack for some reason */
if (stack_page == 0)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -590,7 +590,7 @@ static inline void load_sp0(unsigned lon
/* Free all resources held by a thread. */
extern void release_thread(struct task_struct *);

-unsigned long get_wchan(struct task_struct *p);
+unsigned long __get_wchan(struct task_struct *p);

/*
* Generic CPUID function
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -943,13 +943,10 @@ unsigned long arch_randomize_brk(struct
* because the task might wake up and we might look at a stack
* changing under us.
*/
-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long entry = 0;

- if (p == current || task_is_running(p))
- return 0;
-
stack_trace_save_tsk(p, &entry, 1, 0);
return entry;
}
--- a/arch/xtensa/include/asm/processor.h
+++ b/arch/xtensa/include/asm/processor.h
@@ -215,7 +215,7 @@ struct mm_struct;
/* Free all resources held by a thread. */
#define release_thread(thread) do { } while(0)

-extern unsigned long get_wchan(struct task_struct *p);
+extern unsigned long __get_wchan(struct task_struct *p);

#define KSTK_EIP(tsk) (task_pt_regs(tsk)->pc)
#define KSTK_ESP(tsk) (task_pt_regs(tsk)->areg[1])
--- a/arch/xtensa/kernel/process.c
+++ b/arch/xtensa/kernel/process.c
@@ -298,15 +298,12 @@ int copy_thread(unsigned long clone_flag
* These bracket the sleeping functions..
*/

-unsigned long get_wchan(struct task_struct *p)
+unsigned long __get_wchan(struct task_struct *p)
{
unsigned long sp, pc;
unsigned long stack_page = (unsigned long) task_stack_page(p);
int count = 0;

- if (!p || p == current || task_is_running(p))
- return 0;
-
sp = p->thread.sp;
pc = MAKE_PC_FROM_RA(p->thread.ra, p->thread.sp);

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2139,6 +2139,7 @@ static inline void set_task_cpu(struct t
#endif /* CONFIG_SMP */

extern bool sched_task_on_rq(struct task_struct *p);
+extern unsigned long get_wchan(struct task_struct *p);

/*
* In order to reduce various lock holder preemption latencies provide an
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1962,6 +1962,25 @@ bool sched_task_on_rq(struct task_struct
return task_on_rq_queued(p);
}

+unsigned long get_wchan(struct task_struct *p)
+{
+ unsigned long ip = 0;
+ unsigned int state;
+
+ if (!p || p == current)
+ return 0;
+
+ /* Only get wchan if task is blocked and we can keep it that way. */
+ raw_spin_lock_irq(&p->pi_lock);
+ state = READ_ONCE(p->__state);
+ smp_rmb(); /* see try_to_wake_up() */
+ if (state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq)
+ ip = __get_wchan(p);
+ raw_spin_unlock_irq(&p->pi_lock);
+
+ return ip;
+}
+
static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
{
if (!(flags & ENQUEUE_NOCLOCK))