[v5,01/10] nfsd: Protect the nfs4_file delegation fields using the fi_lock

Commit Message

Jeff Layton July 21, 2014, 1:34 p.m. UTC

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.

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If it has, then we assume that the lease is no longer valid and that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 <[e-mail]>
Signed-off-by: Jeff Layton <[e-mail]>
---
 fs/nfsd/nfs4state.c | 89 ++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 65 insertions(+), 24 deletions(-)

Comments

Christoph Hellwig July 21, 2014, 3:51 p.m. UTC | #1

Looks good,

Reviewed-by: Christoph Hellwig <[e-mail]>
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Patch

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index fd4deb049ddf..b05ac229fff0 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 +3504,76 @@  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:
+	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)