linux-kernel - Re: devpts mounts too slowly

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Message-Id: <20090624145822.72aaaff6.akpm@linux-foundation.org>
Date:	Wed, 24 Jun 2009 14:58:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	hpa@...or.com, ray-lk@...rabbit.org, renton@...ton.name,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: devpts mounts too slowly

On Wed, 24 Jun 2009 21:01:08 +0100
Al Viro <viro@...IV.linux.org.uk> wrote:

> On Wed, Jun 10, 2009 at 01:51:25PM -0700, H. Peter Anvin wrote:
> > Andrew Morton wrote:
> > > 
> > > hm, OK.
> > > 
> > > I've now mounted 15000 devpts's and still no slowdown is evident.
> > 
> > I ran my test script, mounting ramfs, with n=100000, and well, gave up
> > since it hadn't gotten any further than 57000 or so overnight.  At that
> > time each individual mount was taking several seconds.
> > 
> > Graphing the delays seem to indicate O(n^2) behavior.
> > 
> > umounts do not appear affected; each umount still take negible time.
> 
> I think I know what's going on.  /sbin/mount is linked against libselinux
> /sbin/umount is not.  And FPOS in question blows if you
> 	* do not have selinuxfs mounted (e.g. because selinux is not enabled)
> 	* have a lot of mounts.
> 
> What happens is that this piece of crap checks for presence of selinuxfs
> on /selinux; then, if the thing isn't there, we go and scan the entire
> /proc/mounts in search of selinuxfs mounts.
> 
> If akpm has selinux enabled on his testbox and you don't have it on yours,
> we have all observations explained.

CONFIG_SECURITY_SELINUX=y
CONFIG_SECURITY_SELINUX_BOOTPARAM=y
CONFIG_SECURITY_SELINUX_BOOTPARAM_VALUE=1
CONFIG_SECURITY_SELINUX_DISABLE=y
CONFIG_SECURITY_SELINUX_DEVELOP=y
CONFIG_SECURITY_SELINUX_AVC_STATS=y
CONFIG_SECURITY_SELINUX_CHECKREQPROT_VALUE=1
# CONFIG_SECURITY_SELINUX_ENABLE_SECMARK_DEFAULT is not set
# CONFIG_SECURITY_SELINUX_POLICYDB_VERSION_MAX is not set

>  I'd expect similar slowdown from
> ls on an empty directory, BTW - /bin/ls is linked against the same thing,
> so it gets hit as well.  Before it even gets to main().
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