Messages in this thread | | | Date | Mon, 13 Jun 2022 14:38:07 -0500 | From | Tyler Hicks <> | Subject | Re: [PATCH v2 1/5] 9p: Fix refcounting during full path walks for fid lookups |
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On 2022-06-12 08:17:16, Dominique Martinet wrote: > Tyler Hicks wrote on Thu, May 26, 2022 at 06:59:59PM -0500: > > Decrement the refcount of the parent dentry's fid after walking > > each path component during a full path walk for a lookup. Failure to do > > so can lead to fids that are not clunked until the filesystem is > > unmounted, as indicated by this warning: > > > > 9pnet: found fid 3 not clunked > > > > The improper refcounting after walking resulted in open(2) returning > > -EIO on any directories underneath the mount point when using the virtio > > transport. When using the fd transport, there's no apparent issue until > > the filesytem is unmounted and the warning above is emitted to the logs. > > > > In some cases, the user may not yet be attached to the filesystem and a > > new root fid, associated with the user, is created and attached to the > > root dentry before the full path walk is performed. Increment the new > > root fid's refcount to two in that situation so that it can be safely > > decremented to one after it is used for the walk operation. The new fid > > will still be attached to the root dentry when > > v9fs_fid_lookup_with_uid() returns so a final refcount of one is > > correct/expected. > > > > Fixes: 6636b6dcc3db ("9p: add refcount to p9_fid struct") > > Cc: stable@vger.kernel.org > > Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com> > > --- > > fs/9p/fid.c | 17 +++++------------ > > 1 file changed, 5 insertions(+), 12 deletions(-) > > > > diff --git a/fs/9p/fid.c b/fs/9p/fid.c > > index 79df61fe0e59..5a469b79c1ee 100644 > > --- a/fs/9p/fid.c > > +++ b/fs/9p/fid.c > > @@ -152,7 +152,7 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry, > > const unsigned char **wnames, *uname; > > int i, n, l, clone, access; > > struct v9fs_session_info *v9ses; > > - struct p9_fid *fid, *old_fid = NULL; > > + struct p9_fid *fid, *old_fid; > > > > v9ses = v9fs_dentry2v9ses(dentry); > > access = v9ses->flags & V9FS_ACCESS_MASK; > > @@ -194,13 +194,12 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry, > > if (IS_ERR(fid)) > > return fid; > > > > + refcount_inc(&fid->count); > > v9fs_fid_add(dentry->d_sb->s_root, fid); > > } > > /* If we are root ourself just return that */ > > - if (dentry->d_sb->s_root == dentry) { > > - refcount_inc(&fid->count); > > + if (dentry->d_sb->s_root == dentry) > > return fid; > > - } > > /* > > * Do a multipath walk with attached root. > > * When walking parent we need to make sure we > > @@ -212,6 +211,7 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry, > > fid = ERR_PTR(n); > > goto err_out; > > } > > + old_fid = fid; > > clone = 1; > > i = 0; > > while (i < n) { > > @@ -221,15 +221,8 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry, > > * walk to ensure none of the patch component change > > */ > > fid = p9_client_walk(fid, l, &wnames[i], clone); > > + p9_client_clunk(old_fid); > > hmm, if we're not cloning then fid == old_fid and the refcount is not > increased? (I think... I didn't even realize/remember that walk had a > no-clone mode, sorry.) > > So we'd only need to clunk if old fid here if we're cloning (old fid is > the initial root fid), but I'm not sure how to test this path as I > couldn't think of any pattern that'd trigger a multi-level lookup, > so I'm not 100% sure; I'll try a bit more.
Yes, you're correct. Nice catch!
Tyler
> > -- > Dominique >
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