On Mon, 21 Jul 2014 17:05:31 -0400
"J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> On Fri, Jul 18, 2014 at 03:21:49PM -0400, J. Bruce Fields wrote:
> > On Fri, Jul 18, 2014 at 03:04:04PM -0400, Jeff Layton wrote:
> > > On Fri, 18 Jul 2014 13:49:57 -0400
> > > "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> > >
> > > > On Fri, Jul 18, 2014 at 01:31:40PM -0400, Jeff Layton wrote:
> > > > > On Fri, 18 Jul 2014 12:28:25 -0400
> > > > > "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> > > > >
> > > > > > On Fri, Jul 18, 2014 at 11:13:27AM -0400, Jeff Layton wrote:
> > > > > > > Move more of the delegation fields to be protected by the fi_lock. It's
> > > > > > > more granular than the state_lock and in later patches we'll want to
> > > > > > > be able to rely on it in addition to the state_lock.
> > > > > > >
> > > > > > > Also, the current code in nfs4_setlease calls vfs_setlease and uses the
> > > > > > > client_mutex to ensure that it doesn't disappear before we can hash the
> > > > > > > delegation. With the client_mutex gone, we'll have a potential race
> > > > > > > condition.
> > > > > > >
> > > > > > > It's possible that the delegation could be recalled after we acquire the
> > > > > > > lease but before we ever get around to hashing it. If that happens, then
> > > > > > > we'd have a nfs4_file that *thinks* it has a delegation, when it
> > > > > > > actually has none.
> > > > > >
> > > > > > I understand now, thanks: so the lease break code walks the list of
> > > > > > delegations associated with the file, finds none, and issues no recall,
> > > > > > but the open code continues merrily on and returns a delegation, with
> > > > > > the result that we return the client a delegation that will never be
> > > > > > recalled.
> > > > > >
> > > > > > That could be worded more carefully, and would be worth a separate patch
> > > > > > (since the bug predates the new locking).
> > > > > >
> > > > >
> > > > > Yes, that's basically correct. I'd have to think about how to fix that
> > > > > with the current code. It's probably doable if you think it's
> > > > > worthwhile, but I'll need to rebase this set on top of it.
> > > >
> > > > Well, I was wondering if this patch could just be split in two, no need
> > > > to backport further than that.
> > > >
> > >
> > > Erm, now that I've looked, I don't think it'll be that easy. The key
> > > here is to ensure that fi_had_conflict is set while holding the
> > > fi_lock. The trick here is that we need to take it in nfs4_setlease as
> > > well, and check the flag before hashing the delegation without dropping
> > > the fi_lock.
> >
> > OK, I'll live. For the sake of anyone that actually runs across that
> > bug I'll update the summary and changelog to emphasize the bugfix over
> > the locking change.
>
> So, intending to apply as follows.
>
> --b.
>
> commit 417c6629b2d81d5a18d29c4bbb6a9a4c64282a36
> Author: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
> Date: Mon Jul 21 09:34:57 2014 -0400
>
> nfsd: fix race that grants unrecallable delegation
>
> If nfs4_setlease succesfully acquires a new delegation, then another
> task breaks the delegation before we reach hash_delegation_locked, then
> the breaking task will see an empty fi_delegations list and do nothing.
> The client will receive an open reply incorrectly granting a delegation
> and will never receive a recall.
>
> Move more of the delegation fields to be protected by the fi_lock. It's
> more granular than the state_lock and in later patches we'll want to
> be able to rely on it in addition to the state_lock.
>
> Attempt to acquire a delegation. If that succeeds, take the spinlocks
> and then check to see if the file has had a conflict show up since then.
> If it has, then we assume that the lease is no longer valid and that
> we shouldn't hand out a delegation.
>
> There's also one more potential (but very unlikely) problem. If the
> lease is broken before the delegation is hashed, then it could leak.
> In the event that the fi_delegations list is empty, reset the
> fl_break_time to jiffies so that it's cleaned up ASAP by
> the normal lease handling code.
>
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 10cdb67..cc477dd 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -624,6 +624,8 @@ nfs4_put_delegation(struct nfs4_delegation *dp)
>
> static void nfs4_put_deleg_lease(struct nfs4_file *fp)
> {
> + lockdep_assert_held(&state_lock);
> +
> if (!fp->fi_lease)
> return;
> if (atomic_dec_and_test(&fp->fi_delegees)) {
> @@ -643,11 +645,10 @@ static void
> hash_delegation_locked(struct nfs4_delegation *dp, struct nfs4_file *fp)
> {
> lockdep_assert_held(&state_lock);
> + lockdep_assert_held(&fp->fi_lock);
>
> dp->dl_stid.sc_type = NFS4_DELEG_STID;
> - spin_lock(&fp->fi_lock);
> list_add(&dp->dl_perfile, &fp->fi_delegations);
> - spin_unlock(&fp->fi_lock);
> list_add(&dp->dl_perclnt, &dp->dl_stid.sc_client->cl_delegations);
> }
>
> @@ -659,17 +660,18 @@ unhash_delegation(struct nfs4_delegation *dp)
>
> spin_lock(&state_lock);
> dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID;
> + spin_lock(&fp->fi_lock);
> list_del_init(&dp->dl_perclnt);
> list_del_init(&dp->dl_recall_lru);
> - spin_lock(&fp->fi_lock);
> list_del_init(&dp->dl_perfile);
> spin_unlock(&fp->fi_lock);
> - spin_unlock(&state_lock);
> if (fp) {
> nfs4_put_deleg_lease(fp);
> - put_nfs4_file(fp);
> dp->dl_file = NULL;
> }
> + spin_unlock(&state_lock);
> + if (fp)
> + put_nfs4_file(fp);
> }
>
> static void destroy_revoked_delegation(struct nfs4_delegation *dp)
> @@ -3141,10 +3143,19 @@ static void nfsd_break_deleg_cb(struct file_lock *fl)
> */
> fl->fl_break_time = 0;
>
> - fp->fi_had_conflict = true;
> spin_lock(&fp->fi_lock);
> - list_for_each_entry(dp, &fp->fi_delegations, dl_perfile)
> - nfsd_break_one_deleg(dp);
> + fp->fi_had_conflict = true;
> + /*
> + * If there are no delegations on the list, then we can't count on this
> + * lease ever being cleaned up. Set the fl_break_time to jiffies so that
> + * time_out_leases will do it ASAP. The fact that fi_had_conflict is now
> + * true should keep any new delegations from being hashed.
> + */
> + if (list_empty(&fp->fi_delegations))
> + fl->fl_break_time = jiffies;
> + else
> + list_for_each_entry(dp, &fp->fi_delegations, dl_perfile)
> + nfsd_break_one_deleg(dp);
> spin_unlock(&fp->fi_lock);
> }
>
> @@ -3491,46 +3502,77 @@ static int nfs4_setlease(struct nfs4_delegation *dp)
> {
> struct nfs4_file *fp = dp->dl_file;
> struct file_lock *fl;
> - int status;
> + struct file *filp;
> + int status = 0;
>
> fl = nfs4_alloc_init_lease(fp, NFS4_OPEN_DELEGATE_READ);
> if (!fl)
> return -ENOMEM;
> - fl->fl_file = find_readable_file(fp);
> - status = vfs_setlease(fl->fl_file, fl->fl_type, &fl);
> - if (status)
> - goto out_free;
> + filp = find_readable_file(fp);
> + if (!filp) {
> + /* We should always have a readable file here */
> + WARN_ON_ONCE(1);
> + return -EBADF;
> + }
> + fl->fl_file = filp;
> + status = vfs_setlease(filp, fl->fl_type, &fl);
> + if (status) {
> + locks_free_lock(fl);
> + goto out_fput;
> + }
> + spin_lock(&state_lock);
> + spin_lock(&fp->fi_lock);
> + /* Did the lease get broken before we took the lock? */
> + status = -EAGAIN;
> + if (fp->fi_had_conflict)
> + goto out_unlock;
> + /* Race breaker */
> + if (fp->fi_lease) {
> + status = 0;
> + atomic_inc(&fp->fi_delegees);
> + hash_delegation_locked(dp, fp);
> + goto out_unlock;
> + }
> fp->fi_lease = fl;
> - fp->fi_deleg_file = fl->fl_file;
> + fp->fi_deleg_file = filp;
> atomic_set(&fp->fi_delegees, 1);
> - spin_lock(&state_lock);
> hash_delegation_locked(dp, fp);
> + spin_unlock(&fp->fi_lock);
> spin_unlock(&state_lock);
> return 0;
> -out_free:
> - if (fl->fl_file)
> - fput(fl->fl_file);
> - locks_free_lock(fl);
> +out_unlock:
> + spin_unlock(&fp->fi_lock);
> + spin_unlock(&state_lock);
> +out_fput:
> + fput(filp);
> return status;
> }
>
> static int nfs4_set_delegation(struct nfs4_delegation *dp, struct nfs4_file *fp)
> {
> + int status = 0;
> +
> if (fp->fi_had_conflict)
> return -EAGAIN;
> get_nfs4_file(fp);
> + spin_lock(&state_lock);
> + spin_lock(&fp->fi_lock);
> dp->dl_file = fp;
> - if (!fp->fi_lease)
> + if (!fp->fi_lease) {
> + spin_unlock(&fp->fi_lock);
> + spin_unlock(&state_lock);
> return nfs4_setlease(dp);
> - spin_lock(&state_lock);
> + }
> atomic_inc(&fp->fi_delegees);
> if (fp->fi_had_conflict) {
> - spin_unlock(&state_lock);
> - return -EAGAIN;
> + status = -EAGAIN;
> + goto out_unlock;
> }
> hash_delegation_locked(dp, fp);
> +out_unlock:
> + spin_unlock(&fp->fi_lock);
> spin_unlock(&state_lock);
> - return 0;
> + return status;
> }
>
> static void nfsd4_open_deleg_none_ext(struct nfsd4_open *open, int status)
Looks good -- ACK. Thanks for fixing that up...
--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
