linux-kernel - Re: [PATCH] TRACING: FTRACE: Use xarray structure for ftrace syscalls

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Date:   Tue, 22 Oct 2019 15:51:04 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Hassan Naveed <hnaveed@...ecomp.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Paul Burton <pburton@...ecomp.com>
Subject: Re: [PATCH] TRACING: FTRACE: Use xarray structure for ftrace
 syscalls

On Tue, 22 Oct 2019 18:24:25 +0000
Hassan Naveed <hnaveed@...ecomp.com> wrote:


Nit, the subject should simply be:

 "tracing: Use xarray for syscall trace events"


> Signed-off-by: Hassan Naveed <hnaveed@...ecomp.com>
> ---
>  kernel/trace/trace_syscalls.c | 17 ++++-------------
>  1 file changed, 4 insertions(+), 13 deletions(-)
> 
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index f93a56d2db27..1fee710be874 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -7,6 +7,7 @@
>  #include <linux/module.h>	/* for MODULE_NAME_LEN via KSYM_SYMBOL_LEN */
>  #include <linux/ftrace.h>
>  #include <linux/perf_event.h>
> +#include <linux/xarray.h>
>  #include <asm/syscall.h>
>  
>  #include "trace_output.h"
> @@ -30,7 +31,7 @@ syscall_get_enter_fields(struct trace_event_call *call)
>  extern struct syscall_metadata *__start_syscalls_metadata[];
>  extern struct syscall_metadata *__stop_syscalls_metadata[];
>  
> -static struct syscall_metadata **syscalls_metadata;
> +static DEFINE_XARRAY(syscalls_metadata);
>  
>  #ifndef ARCH_HAS_SYSCALL_MATCH_SYM_NAME
>  static inline bool arch_syscall_match_sym_name(const char *sym, const char *name)
> @@ -101,10 +102,7 @@ find_syscall_meta(unsigned long syscall)
>  
>  static struct syscall_metadata *syscall_nr_to_meta(int nr)
>  {
> -	if (!syscalls_metadata || nr >= NR_syscalls || nr < 0)
> -		return NULL;
> -
> -	return syscalls_metadata[nr];
> +	return xa_load(&syscalls_metadata, (unsigned long)nr);
>  }
>  
>  const char *get_syscall_name(int syscall)
> @@ -535,13 +533,6 @@ void __init init_ftrace_syscalls(void)
>  	unsigned long addr;
>  	int i;
>  
> -	syscalls_metadata = kcalloc(NR_syscalls, sizeof(*syscalls_metadata),
> -				    GFP_KERNEL);
> -	if (!syscalls_metadata) {
> -		WARN_ON(1);
> -		return;
> -	}
> -
>  	for (i = 0; i < NR_syscalls; i++) {
>  		addr = arch_syscall_addr(i);
>  		meta = find_syscall_meta(addr);
> @@ -549,7 +540,7 @@ void __init init_ftrace_syscalls(void)
>  			continue;
>  
>  		meta->syscall_nr = i;
> -		syscalls_metadata[i] = meta;
> +		xa_store(&syscalls_metadata, i, meta, GFP_KERNEL);

Shouldn't xa_store() return be tested for memory failure?

-- Steve

>  	}
>  }
>