> > On Thu, Jan 16, 2020 at 09:25:42PM +0900, Misono Tomohiro wrote:
> > > > From: Stefan Hajnoczi <stefa...@redhat.com>
> > > >
> > > > If thread A is using an inode it must not be deleted by thread B
> > > > when processing a FUSE_FORGET request.
> > > >
> > > > The FUSE protocol itself already has a counter called nlookup that
> > > > is used in FUSE_FORGET messages. We cannot trust this counter
> > > > since the untrusted client can manipulate it via FUSE_FORGET messages.
> > > >
> > > > Introduce a new refcount to keep inodes alive for the required lifespan.
> > > > lo_inode_put() must be called to release a reference. FUSE's
> > > > nlookup counter holds exactly one reference so that the inode
> > > > stays alive as long as the client still wants to remember it.
> > > >
> > > > Note that the lo_inode->is_symlink field is moved to avoid
> > > > creating a hole in the struct due to struct field alignment.
> > > >
> > > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> > > > ---
> > > > tools/virtiofsd/passthrough_ll.c | 168
> > > > ++++++++++++++++++++++++++-----
> > > > 1 file changed, 145 insertions(+), 23 deletions(-)
> > > >
> > > > diff --git a/tools/virtiofsd/passthrough_ll.c
> > > > b/tools/virtiofsd/passthrough_ll.c
> > > > index b19c9ee328..8f4ab8351c 100644
> > > > --- a/tools/virtiofsd/passthrough_ll.c
> > > > +++ b/tools/virtiofsd/passthrough_ll.c
> > > > @@ -99,7 +99,13 @@ struct lo_key {
> > > >
> > > > struct lo_inode {
> > > > int fd;
> > > > - bool is_symlink;
> > > > +
> > > > + /*
> > > > + * Atomic reference count for this object. The nlookup field
> > > > holds a
> > > > + * reference and release it when nlookup reaches 0.
> > > > + */
> > > > + gint refcount;
> > > > +
> > > > struct lo_key key;
> > > >
> > > > /*
> > > > @@ -118,6 +124,8 @@ struct lo_inode {
> > > > fuse_ino_t fuse_ino;
> > > > pthread_mutex_t plock_mutex;
> > > > GHashTable *posix_locks; /* protected by
> > > > lo_inode->plock_mutex */
> > > > +
> > > > + bool is_symlink;
> > > > };
> > > >
> > > > struct lo_cred {
> > > > @@ -473,6 +481,23 @@ static ssize_t lo_add_inode_mapping(fuse_req_t
> > > > req, struct lo_inode *inode)
> > > > return elem - lo_data(req)->ino_map.elems; }
> > > >
> > > > +static void lo_inode_put(struct lo_data *lo, struct lo_inode
> > > > +**inodep) {
> > > > + struct lo_inode *inode = *inodep;
> > > > +
> > > > + if (!inode) {
> > > > + return;
> > > > + }
> > > > +
> > > > + *inodep = NULL;
> > > > +
> > > > + if (g_atomic_int_dec_and_test(&inode->refcount)) {
> > > > + close(inode->fd);
> > > > + free(inode);
> > > > + }
> > > > +}
> > > > +
> > > > +/* Caller must release refcount using lo_inode_put() */
> > > > static struct lo_inode *lo_inode(fuse_req_t req, fuse_ino_t ino)
> > > > {
> > > > struct lo_data *lo = lo_data(req); @@ -480,6 +505,9 @@ static
> > > > struct lo_inode *lo_inode(fuse_req_t req, fuse_ino_t ino)
> > > >
> > > > pthread_mutex_lock(&lo->mutex);
> > > > elem = lo_map_get(&lo->ino_map, ino);
> > > > + if (elem) {
> > > > + g_atomic_int_inc(&elem->inode->refcount);
> > > > + }
> > > > pthread_mutex_unlock(&lo->mutex);
> > > >
> > > > if (!elem) {
> > > > @@ -489,10 +517,23 @@ static struct lo_inode *lo_inode(fuse_req_t req,
> > > > fuse_ino_t ino)
> > > > return elem->inode;
> > > > }
> > > >
> > > > +/*
> > > > + * TODO Remove this helper and force callers to hold an inode
> > > > +refcount until
> > > > + * they are done with the fd. This will be done in a later patch
> > > > +to make
> > > > + * review easier.
> > > > + */
> > > > static int lo_fd(fuse_req_t req, fuse_ino_t ino) {
> > > > struct lo_inode *inode = lo_inode(req, ino);
> > > > - return inode ? inode->fd : -1;
> > > > + int fd;
> > > > +
> > > > + if (!inode) {
> > > > + return -1;
> > > > + }
> > > > +
> > > > + fd = inode->fd;
> > > > + lo_inode_put(lo_data(req), &inode);
> > > > + return fd;
> > > > }
> > > >
> > > > static void lo_init(void *userdata, struct fuse_conn_info *conn)
> > > > @@ -547,6 +588,10 @@ static void lo_getattr(fuse_req_t req, fuse_ino_t
> > > > ino,
> > > > fuse_reply_attr(req, &buf, lo->timeout); }
> > > >
> > > > +/*
> > > > + * Increments parent->nlookup and caller must release refcount
> > > > +using
> > > > + * lo_inode_put(&parent).
> > > > + */
> > > > static int lo_parent_and_name(struct lo_data *lo, struct lo_inode
> > > > *inode,
> > > > char path[PATH_MAX], struct
> > > > lo_inode **parent) { @@ -584,6 +629,7 @@ retry:
> > > > p = &lo->root;
> > > > pthread_mutex_lock(&lo->mutex);
> > > > p->nlookup++;
> > > > + g_atomic_int_inc(&p->refcount);
> > > > pthread_mutex_unlock(&lo->mutex);
> > > > } else {
> > > > *last = '\0';
> > >
> > > We need lo_ionde_put() in error path, right?:
> > > https://gitlab.com/virtio-fs/qemu/blob/virtio-fs-as-posted-2019-12-1
> > > 2/tools/virtiofsd/passthrough_ll.c#L680
> >
> > Yes, thanks for spotting this bug! The lo_parent_and_name() code
> > should look like this:
> >
> > fail_unref:
> > unref_inode_lolocked(lo, p, 1);
> > lo_inode_put(lo, &p);
> > ...
>
> I've merged that one in.
Thanks, so with that:
Reviewed-by: Misono Tomohiro <misono.tomoh...@jp.fujitsu.com>
>
> > > nit: if yes, unref_inode_lolocked() is always paired with lo_inode_put().
> > > So how about combine them in one function? As p->nloockup and
> > > p->refcount are both incremented in one place
> > > (lo_find/lo_parent_and_name) in these case, it seems natural for me to
> > > decrement them in one function as well.
> >
> > Nice idea. I would also drop the nlookup argument - this function
> > will only be used with nlookup=1.
>
> I'll leave that to you if you want to send a patch on top.
>
> Dave
>
> > Stefan
>
>
> --
> Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
