Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:47226 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760930AbaGRQ2b (ORCPT ); Fri, 18 Jul 2014 12:28:31 -0400 Date: Fri, 18 Jul 2014 12:28:25 -0400 From: "J. Bruce Fields" To: Jeff Layton Cc: hch@infradead.org, linux-nfs@vger.kernel.org Subject: Re: [PATCH v4 01/10] nfsd: Protect the nfs4_file delegation fields using the fi_lock Message-ID: <20140718162825.GA8811@fieldses.org> References: <1405696416-32585-1-git-send-email-jlayton@primarydata.com> <1405696416-32585-2-git-send-email-jlayton@primarydata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1405696416-32585-2-git-send-email-jlayton@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: 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). > 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 If it has, then we assume that the lease is no longer valid and that 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. Is there actually any guarantee time_out_leases() will get called on this inode again? --b. > > Signed-off-by: Trond Myklebust > Signed-off-by: Jeff Layton > --- > fs/nfsd/nfs4state.c | 90 +++++++++++++++++++++++++++++++++++++++-------------- > 1 file changed, 66 insertions(+), 24 deletions(-) > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > index fd4deb049ddf..9ab067e85b51 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) > @@ -3143,10 +3145,19 @@ 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); > } > > @@ -3493,46 +3504,77 @@ 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; > + } > + 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: > + if (filp) > + 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) > -- > 1.9.3 >