linux-kernel - Re: lost path_put in perf_fill_ns_link

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Date:   Tue, 7 Nov 2017 11:03:19 -0800
From:   Andrei Vagin <avagin@...tuozzo.com>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     linux-kernel@...r.kernel.org,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: lost path_put in perf_fill_ns_link_info

Hi Vasily and all,

The patch looks correct for me. I tried to reproduce this issue and
checked that this patch fixes it. Bellow you can find my test program
and a command line to run it. The problem still exists even with this patch.

$ cat test.c
#define _GNU_SOURCE
#include <sched.h>

int main(int argc, char **argv)
{
	while (1)
		unshare(CLONE_NEWUTS);
	return 0;
}

$ gcc -o test_unshare test.c
$ for i in `seq 10000`; do perf trace -o log unshare -u true; done &
[5] 28766
$ for i in `seq 10000`; do perf trace -o log unshare -u true; done &
[6] 28840

$ echo 3 > /proc/sys/vm/drop_caches | cat /proc/slabinfo | grep dentry
dentry             74848  78660    224   18    1 : tunables    0    0    0 : slabdata   4370   4370      0

$ sleep 10
$ echo 3 > /proc/sys/vm/drop_caches | cat /proc/slabinfo | grep dentry
dentry             75145  79002    224   18    1 : tunables    0    0    0 : slabdata   4389   4389      0

$ sleep 10
$ echo 3 > /proc/sys/vm/drop_caches | cat /proc/slabinfo | grep dentry
dentry             75921  79776    224   18    1 : tunables    0    0    0 : slabdata   4432   4432      0
$ git log --pretty=oneline | head -n 2
c83bceb10b36cef895def4b2dfe0aff6ca7c9784 lost path_put in perf_fill_ns_link_info
8b82a8a7ab53ee1a065ac69c835737a701f46b2e Add linux-next specific files for 20171107

Thanks,
Andrei

On Mon, Nov 06, 2017 at 09:22:18AM +0300, Vasily Averin wrote:
> Fixes: commit e422267322cd ("perf: Add PERF_RECORD_NAMESPACES to include namespaces related info")
> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
> ---
>  kernel/events/core.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 10cdb9c..ab5ac84 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6756,6 +6756,7 @@ static void perf_fill_ns_link_info(struct perf_ns_link_info *ns_link_info,
>  		ns_inode = ns_path.dentry->d_inode;
>  		ns_link_info->dev = new_encode_dev(ns_inode->i_sb->s_dev);
>  		ns_link_info->ino = ns_inode->i_ino;
> +		path_put(&ns_path);
>  	}
>  }
>