netdev - Re: [PATCH] prevent the read ahead of /proc/slabinfo in ss take 2

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1423543769.28434.2.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 09 Feb 2015 20:49:29 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Bryton Lee <brytonlee01@...il.com>
Cc:	stephen@...workplumber.org, netdev@...r.kernel.org,
	davem@...emloft.net
Subject: Re: [PATCH] prevent the read ahead of /proc/slabinfo in ss take 2

On Tue, 2015-02-10 at 10:46 +0800, Bryton Lee wrote:
> ss reads ahead of /proc/slabinfo whatever slabstat will be used or not in future.
> this will cause huge system delay when the kernel hires SLAB allocator(SLUB allocator is ok). when program reads
> /proc/slabinfo, it will call s_show() in SLAB allocator level, and s_show() calls spin_lock_irq(&l3->list_lock)
> then iterate on whole three lists. if one slab has about 900 million objects (for example dentry),
> it will cause more than 1000ms delay.
> 

Please keep lengths < 70 chars in changelog.

> so this patch prevents the read ahead of /proc/slabinfo, ss runs with most parameters not using slabstat at all.
> and this patch also change slabstat and slabstat_valid to static.
> 
> Signed-off-by: Bryton Lee <brytonlee01@...il.com>
> ---
>  misc/ss.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/misc/ss.c b/misc/ss.c
> index 7fc0a99..5fa6259 100644
> --- a/misc/ss.c
> +++ b/misc/ss.c
> @@ -616,7 +616,8 @@ struct slabstat
>  	int skbs;
>  };
>  
> -struct slabstat slabstat;
> +static struct slabstat slabstat;
> +static int slabstat_valid = 0;

David pointed that you never set this variable to 1 or any value...

Why is this variable needed, if its content is known/constant ?


I presume you wanted to set it in get_slabstat(), right ?

>  
>  static const char *slabstat_ids[] =
>  {
> @@ -2230,6 +2231,9 @@ static int tcp_show(struct filter *f, int socktype)
>  	 * it is able to give us some memory for snapshot.
>  	 */
>  	if (1) {
> +		if (!slabstat_valid)
> +			get_slabstat(&slabstat);
> +
>  		int guess = slabstat.socks+slabstat.tcp_syns;
>  		if (f->states&(1<<SS_TIME_WAIT))
>  			guess += slabstat.tcp_tws;
> @@ -3196,6 +3200,9 @@ static int print_summary(void)
>  	if (get_snmp_int("Tcp:", "CurrEstab", &sn.tcp_estab) < 0)
>  		perror("ss: get_snmpstat");
>  
> +	if (!slabstat_valid)
> +		get_slabstat(&slabstat);
> +
>  	printf("Total: %d (kernel %d)\n", s.socks, slabstat.socks);
>  
>  	printf("TCP:   %d (estab %d, closed %d, orphaned %d, synrecv %d, timewait %d/%d), ports %d\n",
> @@ -3543,8 +3550,6 @@ int main(int argc, char *argv[])
>  	argc -= optind;
>  	argv += optind;
>  
> -	get_slabstat(&slabstat);
> -
>  	if (do_summary) {
>  		print_summary();
>  		if (do_default && argc == 0)


--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html