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From: Ian Kent <raven@themaw.net>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	autofs mailing list <autofs@vger.kernel.org>,
	Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Omar Sandoval <osandov@osandov.com>
Subject: Re: [PATCH 6/8] autofs - use path_is_mountpoint() to fix unreliable d_mountpoint() checks
Date: Thu, 27 Oct 2016 10:51:40 +0800	[thread overview]
Message-ID: <1477536700.2898.16.camel@themaw.net> (raw)
In-Reply-To: <20161027021753.GJ19539@ZenIV.linux.org.uk>

On Thu, 2016-10-27 at 03:17 +0100, Al Viro wrote:
> On Tue, Oct 11, 2016 at 01:34:18PM +0800, Ian Kent wrote:
> > 
> > +	path = file->f_path;
> > +
> >  	/*
> >  	 * An empty directory in an autofs file system is always a
> >  	 * mount point. The daemon must have failed to mount this
> > @@ -123,7 +126,7 @@ static int autofs4_dir_open(struct inode *inode, struct
> > file *file)
> >  	 * it.
> >  	 */
> >  	spin_lock(&sbi->lookup_lock);
> > -	if (!d_mountpoint(dentry) && simple_empty(dentry)) {
> > +	if (!path_is_mountpoint(&path) && simple_empty(dentry)) {
> Why not &file->f_path, provided that you constify that thing properly?

Yep, my bad, as pointed out by Eric.

Patches to fix that and constify a bunch of things will follow.

> 
> > 
> > +		if (rcu_walk) {
> > +			if (!path_is_mountpoint_rcu(path))
> > +				return -EISDIR;
> > +		} else {
> > +			if (!path_is_mountpoint(path))
> > +				return -EISDIR;
> IDGI.  What's the point of _having_ the _rcu() variant, anyway?  Here you
> are probably paying more in terms of i-cache footprint/branch prediction
> than you win on not doing that rcu_read_lock()/rcu_read_unlock()...
> 
> _rcu variants make sense when non-RCU case does something you can't do
> under RCU; here your path_is_mountpoint() is pretty close to being
> rcu_read_lock()+path_is_mountpoint_rcu()+rcu_read_unlock() anyway...

Again, my bad, I'll merge these two and post along with the follow up patches
above.

Thanks Al,
Ian

WARNING: multiple messages have this Message-ID (diff)
From: Ian Kent <raven@themaw.net>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	autofs mailing list <autofs@vger.kernel.org>,
	Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Omar Sandoval <osandov@osandov.com>
Subject: Re: [PATCH 6/8] autofs - use path_is_mountpoint() to fix unreliable d_mountpoint() checks
Date: Thu, 27 Oct 2016 10:51:40 +0800	[thread overview]
Message-ID: <1477536700.2898.16.camel@themaw.net> (raw)
In-Reply-To: <20161027021753.GJ19539@ZenIV.linux.org.uk>

On Thu, 2016-10-27 at 03:17 +0100, Al Viro wrote:
> On Tue, Oct 11, 2016 at 01:34:18PM +0800, Ian Kent wrote:
> > 
> > +	path = file->f_path;
> > +
> >  	/*
> >  	 * An empty directory in an autofs file system is always a
> >  	 * mount point. The daemon must have failed to mount this
> > @@ -123,7 +126,7 @@ static int autofs4_dir_open(struct inode *inode, struct
> > file *file)
> >  	 * it.
> >  	 */
> >  	spin_lock(&sbi->lookup_lock);
> > -	if (!d_mountpoint(dentry) && simple_empty(dentry)) {
> > +	if (!path_is_mountpoint(&path) && simple_empty(dentry)) {
> Why not &file->f_path, provided that you constify that thing properly?

Yep, my bad, as pointed out by Eric.

Patches to fix that and constify a bunch of things will follow.

> 
> > 
> > +		if (rcu_walk) {
> > +			if (!path_is_mountpoint_rcu(path))
> > +				return -EISDIR;
> > +		} else {
> > +			if (!path_is_mountpoint(path))
> > +				return -EISDIR;
> IDGI.  What's the point of _having_ the _rcu() variant, anyway?  Here you
> are probably paying more in terms of i-cache footprint/branch prediction
> than you win on not doing that rcu_read_lock()/rcu_read_unlock()...
> 
> _rcu variants make sense when non-RCU case does something you can't do
> under RCU; here your path_is_mountpoint() is pretty close to being
> rcu_read_lock()+path_is_mountpoint_rcu()+rcu_read_unlock() anyway...

Again, my bad, I'll merge these two and post along with the follow up patches
above.

Thanks Al,
Ian
--
To unsubscribe from this list: send the line "unsubscribe autofs" in

  reply	other threads:[~2016-10-27  2:51 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-11  5:33 [PATCH 1/8] vfs - change d_manage() to take a struct path Ian Kent
2016-10-11  5:33 ` [PATCH 2/8] vfs - add path_is_mountpoint() helper Ian Kent
2016-10-11  5:34 ` [PATCH 3/8] vfs - add path_has_submounts() Ian Kent
2016-10-11  5:34 ` [PATCH 4/8] autofs - change autofs4_expire_wait() to take struct path Ian Kent
2016-10-11  5:34 ` [PATCH 5/8] autofs - change autofs4_wait() " Ian Kent
2016-10-11  5:34   ` Ian Kent
2016-10-11  5:34 ` [PATCH 6/8] autofs - use path_is_mountpoint() to fix unreliable d_mountpoint() checks Ian Kent
2016-10-27  2:17   ` Al Viro
2016-10-27  2:51     ` Ian Kent [this message]
2016-10-27  2:51       ` Ian Kent
2016-10-11  5:34 ` [PATCH 7/8] autofs - use path_has_submounts() to fix unreliable have_submount() checks Ian Kent
2016-10-11  5:34   ` Ian Kent
2016-10-11  5:34 ` [PATCH 8/8] vfs - remove unused have_submounts() function Ian Kent
2016-10-11  5:34   ` Ian Kent
2016-10-11 16:04 ` [PATCH 1/8] vfs - change d_manage() to take a struct path Eric W. Biederman
2016-10-11 16:04   ` Eric W. Biederman
2016-10-11 23:47   ` Ian Kent
2016-10-11 23:47     ` Ian Kent
2016-10-19 19:40 ` Andrew Morton
2016-10-20 23:39   ` Ian Kent
2016-10-20 23:39     ` Ian Kent
2016-10-27  2:11     ` Al Viro
2016-10-27  2:11       ` Al Viro
2016-10-27  2:47       ` Ian Kent
2016-10-27  2:47         ` Ian Kent
2016-10-27  6:50         ` Ian Kent
2016-11-01  2:02           ` Ian Kent

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