Re: [PATCH v2 05/10] tracepoints: Migrate to use SYSCALL_WORK flag

[Steven Rostedt]

On Mon, 16 Nov 2020 12:42:01 -0500
Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> wrote:

> For architectures that rely on the generic syscall entry code, use the
> syscall_work field in struct thread_info and the specific SYSCALL_WORK
> flag.  This set of flags has the advantage of being architecture
> independent.
> 
> Users of the flag outside of the generic entry code should rely on the
> accessor macros, such that the flag is still correctly resolved for
> architectures that don't use the generic entry code and still rely on
> TIF flags for system call work.
> 
> Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>

Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

Also added Mathieu to Cc.

-- Steve

> 
> ---
> Changes since v2:
>   - Drop explicit value assignment in enum (tglx)
>   - Avoid FLAG/_FLAG defines (tglx)
>   - Fix comment to refer to SYSCALL_WORK_SECCOMP (me)
> ---
>  include/linux/entry-common.h | 13 +++++--------
>  include/linux/thread_info.h  |  2 ++
>  include/trace/syscall.h      |  6 +++---
>  kernel/entry/common.c        |  4 ++--
>  kernel/trace/trace_events.c  |  8 ++++----
>  kernel/tracepoint.c          |  4 ++--
>  6 files changed, 18 insertions(+), 19 deletions(-)
> 
> diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> index f3fc4457f63f..8aba367e5c79 100644
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -17,10 +17,6 @@
>  # define _TIF_SYSCALL_EMU		(0)
>  #endif
>  
> -#ifndef _TIF_SYSCALL_TRACEPOINT
> -# define _TIF_SYSCALL_TRACEPOINT	(0)
> -#endif
> -
>  #ifndef _TIF_SYSCALL_AUDIT
>  # define _TIF_SYSCALL_AUDIT		(0)
>  #endif
> @@ -46,7 +42,7 @@
>  
>  #define SYSCALL_ENTER_WORK						\
>  	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT  |			\
> -	 _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_EMU |			\
> +	 _TIF_SYSCALL_EMU |						\
>  	 ARCH_SYSCALL_ENTER_WORK)
>  
>  /*
> @@ -58,10 +54,11 @@
>  
>  #define SYSCALL_EXIT_WORK						\
>  	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |			\
> -	 _TIF_SYSCALL_TRACEPOINT | ARCH_SYSCALL_EXIT_WORK)
> +	 ARCH_SYSCALL_EXIT_WORK)
>  
> -#define SYSCALL_WORK_ENTER	(SYSCALL_WORK_SECCOMP)
> -#define SYSCALL_WORK_EXIT	(0)
> +#define SYSCALL_WORK_ENTER	(SYSCALL_WORK_SECCOMP |			\
> +				 SYSCALL_WORK_SYSCALL_TRACEPOINT)
> +#define SYSCALL_WORK_EXIT	(SYSCALL_WORK_SYSCALL_TRACEPOINT)
>  
>  /*
>   * TIF flags handled in exit_to_user_mode_loop()
> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index 1d6488130b5c..ff0ac2ebb4ff 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -37,9 +37,11 @@ enum {
>  
>  enum syscall_work_bit {
>  	SYSCALL_WORK_BIT_SECCOMP,
> +	SYSCALL_WORK_BIT_SYSCALL_TRACEPOINT,
>  };
>  
>  #define SYSCALL_WORK_SECCOMP		BIT(SYSCALL_WORK_BIT_SECCOMP)
> +#define SYSCALL_WORK_SYSCALL_TRACEPOINT	BIT(SYSCALL_WORK_BIT_SYSCALL_TRACEPOINT)
>  
>  #include <asm/thread_info.h>
>  
> diff --git a/include/trace/syscall.h b/include/trace/syscall.h
> index dc8ac27d27c1..8e193f3a33b3 100644
> --- a/include/trace/syscall.h
> +++ b/include/trace/syscall.h
> @@ -37,10 +37,10 @@ struct syscall_metadata {
>  #if defined(CONFIG_TRACEPOINTS) && defined(CONFIG_HAVE_SYSCALL_TRACEPOINTS)
>  static inline void syscall_tracepoint_update(struct task_struct *p)
>  {
> -	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
> -		set_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT);
> +	if (test_syscall_work(SYSCALL_TRACEPOINT))
> +		set_task_syscall_work(p, SYSCALL_TRACEPOINT);
>  	else
> -		clear_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT);
> +		clear_task_syscall_work(p, SYSCALL_TRACEPOINT);
>  }
>  #else
>  static inline void syscall_tracepoint_update(struct task_struct *p)
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index c321056c73d7..4e2b3c08d939 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -63,7 +63,7 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall,
>  	/* Either of the above might have changed the syscall number */
>  	syscall = syscall_get_nr(current, regs);
>  
> -	if (unlikely(ti_work & _TIF_SYSCALL_TRACEPOINT))
> +	if (unlikely(work & SYSCALL_WORK_SYSCALL_TRACEPOINT))
>  		trace_sys_enter(regs, syscall);
>  
>  	syscall_enter_audit(regs, syscall);
> @@ -233,7 +233,7 @@ static void syscall_exit_work(struct pt_regs *regs, unsigned long ti_work,
>  
>  	audit_syscall_exit(regs);
>  
> -	if (ti_work & _TIF_SYSCALL_TRACEPOINT)
> +	if (work & SYSCALL_WORK_SYSCALL_TRACEPOINT)
>  		trace_sys_exit(regs, syscall_get_return_value(current, regs));
>  
>  	step = report_single_step(ti_work);
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 47a71f96e5bc..adf65b502453 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -3428,10 +3428,10 @@ static __init int event_trace_enable(void)
>   * initialize events and perhaps start any events that are on the
>   * command line. Unfortunately, there are some events that will not
>   * start this early, like the system call tracepoints that need
> - * to set the TIF_SYSCALL_TRACEPOINT flag of pid 1. But event_trace_enable()
> - * is called before pid 1 starts, and this flag is never set, making
> - * the syscall tracepoint never get reached, but the event is enabled
> - * regardless (and not doing anything).
> + * to set the %SYSCALL_WORK_SYSCALL_TRACEPOINT flag of pid 1. But
> + * event_trace_enable() is called before pid 1 starts, and this flag
> + * is never set, making the syscall tracepoint never get reached, but
> + * the event is enabled regardless (and not doing anything).
>   */
>  static __init int event_trace_enable_again(void)
>  {
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 3f659f855074..7261fa0f5e3c 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -594,7 +594,7 @@ int syscall_regfunc(void)
>  	if (!sys_tracepoint_refcount) {
>  		read_lock(&tasklist_lock);
>  		for_each_process_thread(p, t) {
> -			set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
> +			set_task_syscall_work(t, SYSCALL_TRACEPOINT);
>  		}
>  		read_unlock(&tasklist_lock);
>  	}
> @@ -611,7 +611,7 @@ void syscall_unregfunc(void)
>  	if (!sys_tracepoint_refcount) {
>  		read_lock(&tasklist_lock);
>  		for_each_process_thread(p, t) {
> -			clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
> +			clear_task_syscall_work(t, SYSCALL_TRACEPOINT);
>  		}
>  		read_unlock(&tasklist_lock);
>  	}