[PATCH] don't invalidate non-directory mountpoints

[PATCH] don't invalidate non-directory mountpoints

[Miklos Szeredi]

d_invalidate allowed a non-directory mountpoint to be invalidated,
which is bad, since the mountpoint becomes unreachable.

I know it's racy wrt attaching/detaching mount, but AFAICS so is
everything else that unhashes the dentry.  This seems to be an
oversight when splitting out vfsmount_lock from dcache_lock.  To be
fixed.

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
---

Index: linux/fs/dcache.c
===================================================================
--- linux.orig/fs/dcache.c	2005-10-04 13:59:57.000000000 +0200
+++ linux/fs/dcache.c	2005-10-07 12:59:11.000000000 +0200
@@ -350,7 +350,8 @@ int d_invalidate(struct dentry * dentry)
 	 */
 	spin_lock(&dentry->d_lock);
 	if (atomic_read(&dentry->d_count) > 1) {
-		if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
+		if (dentry->d_inode && (S_ISDIR(dentry->d_inode->i_mode) ||
+					d_mountpoint(dentry))) {
 			spin_unlock(&dentry->d_lock);
 			spin_unlock(&dcache_lock);
 			return -EBUSY;

Re: [PATCH] don't invalidate non-directory mountpoints

[Al Viro]

On Fri, Oct 07, 2005 at 01:13:50PM +0200, Miklos Szeredi wrote:
> d_invalidate allowed a non-directory mountpoint to be invalidated,
> which is bad, since the mountpoint becomes unreachable.
> 
> I know it's racy wrt attaching/detaching mount, but AFAICS so is
> everything else that unhashes the dentry.  This seems to be an
> oversight when splitting out vfsmount_lock from dcache_lock.  To be
> fixed.

NAK.  That's a wrong way to deal with the problem and it's much older
than vfsmount_lock or dcache_lock (and affects directories too).

Re: [PATCH] don't invalidate non-directory mountpoints

[Miklos Szeredi]

> > d_invalidate allowed a non-directory mountpoint to be invalidated,
> > which is bad, since the mountpoint becomes unreachable.
> > 
> > I know it's racy wrt attaching/detaching mount, but AFAICS so is
> > everything else that unhashes the dentry.  This seems to be an
> > oversight when splitting out vfsmount_lock from dcache_lock.  To be
> > fixed.
> 
> NAK.  That's a wrong way to deal with the problem and it's much older
> than vfsmount_lock or dcache_lock (and affects directories too).

Sorry?

Directories are not invalidated if they have any other reference (like
a mount, or any subdirectories which may have mounts).

So how does it affect directories?

Miklos

Re: [PATCH] don't invalidate non-directory mountpoints

[Al Viro]

On Fri, Oct 07, 2005 at 04:35:53PM +0200, Miklos Szeredi wrote:
> > > d_invalidate allowed a non-directory mountpoint to be invalidated,
> > > which is bad, since the mountpoint becomes unreachable.
> > > 
> > > I know it's racy wrt attaching/detaching mount, but AFAICS so is
> > > everything else that unhashes the dentry.  This seems to be an
> > > oversight when splitting out vfsmount_lock from dcache_lock.  To be
> > > fixed.
> > 
> > NAK.  That's a wrong way to deal with the problem and it's much older
> > than vfsmount_lock or dcache_lock (and affects directories too).
> 
> Sorry?
> 
> Directories are not invalidated if they have any other reference (like
> a mount, or any subdirectories which may have mounts).
> 
> So how does it affect directories?

The underlying problem is still there - parts of mount tree _can_ go
unreachable when remote object dies; trying to pin them down is hopeless
and the only sane way to deal with that is to dissolve the subtrees
of mount when that happens.

Re: [PATCH] don't invalidate non-directory mountpoints

[Miklos Szeredi]

> > > > d_invalidate allowed a non-directory mountpoint to be invalidated,
> > > > which is bad, since the mountpoint becomes unreachable.
> > > > 
> > > > I know it's racy wrt attaching/detaching mount, but AFAICS so is
> > > > everything else that unhashes the dentry.  This seems to be an
> > > > oversight when splitting out vfsmount_lock from dcache_lock.  To be
> > > > fixed.
> > > 
> > > NAK.  That's a wrong way to deal with the problem and it's much older
> > > than vfsmount_lock or dcache_lock (and affects directories too).
> > 
> > Sorry?
> > 
> > Directories are not invalidated if they have any other reference (like
> > a mount, or any subdirectories which may have mounts).
> > 
> > So how does it affect directories?
> 
> The underlying problem is still there - parts of mount tree _can_ go
> unreachable when remote object dies; trying to pin them down is hopeless
> and the only sane way to deal with that is to dissolve the subtrees
> of mount when that happens.

I get it.

Miklos