Re: [PATCH 5/7] sched: Add wrapper for get_wchan() to keep task blocked

Mark Rutland
2021-10-08T12:46:02Z

On Fri, Oct 08, 2021 at 01:15:32PM +0200, Peter Zijlstra wrote:
> From: Kees Cook <keescook@chromium.org>
>
> 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@infradead.org>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

FWIW, this seems to wpork on arm64:

Tested-by: Mark Rutland <mark.rutland@arm.com> [arm64]

Mark.

> ---
> 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))
>
>