linux-kernel - Re: [PATCH] perf:util:dso: Using O_CLOEXEC in do

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Message-ID: <20180115094506.GA14646@krava>
Date:   Mon, 15 Jan 2018 10:45:06 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Wang YanQing <udknight@...il.com>, acme@...hat.com,
        peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf:util:dso: Using O_CLOEXEC in do_open

On Mon, Jan 15, 2018 at 01:04:48PM +0800, Wang YanQing wrote:
> I meet strange behavior with below commands on my gentoo box:
> 1:perf kmem record
> 2:CTRL-C to stop 1
> 3:perf report
> 4:"Enter", "Enter", "Run scripts for all samples",
>   "event_analyzing_sample".
> 
> Then perf report:
> "
> No kallsyms or vmlinux with build-id xxxx was found
> /lib/modules/4.10.0+/build/vmlinux with build id xxxx not found,
> continuing without symbols
> ".
> 
> It is strange because I am sure /lib/modules/4.10.0+/build/vmlinux
> is right for perf.data.
> 
> After digging, I find out the reason is "perf report" generates many
> open fds, then "script_browse" uses popen to run "perf script" which
> run out of open files. The gentoo box has a small default value for
> "max open files", 1024. Yes, "ulimit -n " with a bigger number could
> fix it, but I think that using O_CLOEXEC in do_open is a better way.

that seems right.. so why does kmem record open those
files before calling cmd_record? should that be fixed?

thanks,
jirka

> 
> Signed-off-by: Wang YanQing <udknight@...il.com>
> ---
>  tools/perf/util/dso.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index d5b6f7f..36ef45b 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -446,7 +446,7 @@ static int do_open(char *name)
>  	char sbuf[STRERR_BUFSIZE];
>  
>  	do {
> -		fd = open(name, O_RDONLY);
> +		fd = open(name, O_RDONLY|O_CLOEXEC);
>  		if (fd >= 0)
>  			return fd;
>  
> -- 
> 1.8.5.6.2.g3d8a54e.dirty