Quoting Andrew Morton (akpm@xxxxxxxxxxxxxxxxxxxx):
> On Sat, 20 Feb 2010 04:27:38 -0800 john.johansen@xxxxxxxxxxxxx wrote:
>
> > From: John Johansen <john.johansen@xxxxxxxxxxxxx>
> >
> > When __d_path() hits a lazily unmounted mount point, it tries to prepend
> > the name of the lazily unmounted dentry to the path name. It gets this wrong,
> > and also overwrites the slash that separates the name from the following
> > pathname component. This patch fixes that; if a process was in directory
> > /foo/bar and /foo got lazily unmounted, the old result was ``foobar'' (note the
> > missing slash), while the new result with this patch is ``/foo/bar''.
> >
> > Signed-off-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
> > ---
> > fs/dcache.c | 27 +++++++++++++++++++++++----
> > 1 files changed, 23 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/dcache.c b/fs/dcache.c
> > index 953173a..df49666 100644
> > --- a/fs/dcache.c
> > +++ b/fs/dcache.c
> > @@ -1922,11 +1922,9 @@ char *__d_path(const struct path *path, struct path *root,
> > retval = end-1;
> > *retval = '/';
> >
> > - for (;;) {
> > + while(dentry != root->dentry || vfsmnt != root->mnt) {
>
> Please put a space between the `while' and the `('.
>
> > struct dentry * parent;
> >
> > - if (dentry == root->dentry && vfsmnt == root->mnt)
> > - break;
> > if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
> > /* Global root? */
> > if (vfsmnt->mnt_parent == vfsmnt) {
> > @@ -1950,9 +1948,30 @@ out:
> > return retval;
> >
> > global_root:
> > - retval += 1; /* hit the slash */
> > + /*
> > + * We went past the (vfsmount, dentry) we were looking for and have
> > + * either hit a root dentry, a lazily unmounted dentry, an
> > + * unconnected dentry, or the file is on a pseudo filesystem.
> > + */
> > + if ((dentry->d_sb->s_flags & MS_NOUSER) ||
> > + (dentry->d_name.len = 1 && *dentry->d_name.name == '/')) {
>
> Did you really mean to assign 1 to dentry->d_name.len here? Was `=='
> intended? I hope so, because modifying the dentry in d_path() would be odd.
>
> If this was a mistake then why did the patch pass testing?
Jinkeys! Well I guess it must've passed testing bc that will only be
done for MS_NOUSER filesystems, and we won't later be doing any 'ls'
so the d_name.len isn't really used?
> > + /*
> > + * Historically, we also glue together the root dentry and
> > + * remaining name for pseudo filesystems like pipefs, which
> > + * have the MS_NOUSER flag set. This results in pathnames
> > + * like "pipe:[439336]".
> > + */
> > + retval += 1; /* overwrite the slash */
> > + buflen++;
> > + }
> > if (prepend_name(&retval, &buflen, &dentry->d_name) != 0)
> > goto Elong;
> > +
> > + /* connect lazily unmounted mount point */
> > + if (*retval != '/' && !(dentry->d_sb->s_flags & MS_NOUSER) &&
> > + prepend(&retval, &buflen, "/", 1) != 0)
> > + goto Elong;
> > +
> > root->mnt = vfsmnt;
> > root->dentry = dentry;
> > goto out;
>
> --
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