[PATCH RFC v4 0/2] nfsd: Initial implementation of NFSv4 Courteous Server

[PATCH RFC v4 0/2] nfsd: Initial implementation of NFSv4 Courteous Server

[Dai Ngo]

Hi Bruce,

This series of patches implement the NFSv4 Courteous Server.

A server which does not immediately expunge the state on lease expiration
is known as a Courteous Server.  A Courteous Server continues to recognize
previously generated state tokens as valid until conflict arises between
the expired state and the requests from another client, or the server
reboots.

The v2 patch includes the following:

. add new callback, lm_expire_lock, to lock_manager_operations to
  allow the lock manager to take appropriate action with conflict lock.

. handle conflicts of NFSv4 locks with NFSv3/NLM and local locks.

. expire courtesy client after 24hr if client has not reconnected.

. do not allow expired client to become courtesy client if there are
  waiters for client's locks.

. modify client_info_show to show courtesy client and seconds from
  last renew.

. fix a problem with NFSv4.1 server where the it keeps returning
  SEQ4_STATUS_CB_PATH_DOWN in the successful SEQUENCE reply, after
  the courtesy client re-connects, causing the client to keep sending
  BCTS requests to server.

The v3 patch includes the following:

. modified posix_test_lock to check and resolve conflict locks
  to handle NLM TEST and NFSv4 LOCKT requests.

. separate out fix for back channel stuck in SEQ4_STATUS_CB_PATH_DOWN.

The v4 patch includes:

. rework nfsd_check_courtesy to avoid dead lock of fl_lock and client_lock
  by asking the laudromat thread to destroy the courtesy client.

. handle NFSv4 share reservation conflicts with courtesy client. This
  includes conflicts between access mode and deny mode and vice versa.

. drop the patch for back channel stuck in SEQ4_STATUS_CB_PATH_DOWN.

NOTE: I will submit pynfs tests for courteous server including tests
for share reservation conflicts in a separate patch.

[PATCH RFC v4 1/2] fs/lock: add new callback, lm_expire_lock, to lock_manager_operations

[Dai Ngo]

Add new callback, lm_expire_lock, to lock_manager_operations to allow
the lock manager to take appropriate action to resolve the lock conflict
if possible. The callback takes 2 arguments, file_lock of the blocker
and a testonly flag:

testonly = 1  check and return true if lock conflict can be resolved
              else return false.
testonly = 0  resolve the conflict if possible, return true if conflict
              was resolved esle return false.

Lock manager, such as NFSv4 courteous server, uses this callback to
resolve conflict by destroying lock owner, or the NFSv4 courtesy client
(client that has expired but allowed to maintains its states) that owns
the lock.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
 fs/locks.c         | 26 +++++++++++++++++++++++---
 include/linux/fs.h |  1 +
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 3d6fb4ae847b..893b348a2d57 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -954,6 +954,7 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
 	struct file_lock *cfl;
 	struct file_lock_context *ctx;
 	struct inode *inode = locks_inode(filp);
+	bool ret;
 
 	ctx = smp_load_acquire(&inode->i_flctx);
 	if (!ctx || list_empty_careful(&ctx->flc_posix)) {
@@ -962,11 +963,20 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
 	}
 
 	spin_lock(&ctx->flc_lock);
+retry:
 	list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
-		if (posix_locks_conflict(fl, cfl)) {
-			locks_copy_conflock(fl, cfl);
-			goto out;
+		if (!posix_locks_conflict(fl, cfl))
+			continue;
+		if (cfl->fl_lmops && cfl->fl_lmops->lm_expire_lock &&
+				cfl->fl_lmops->lm_expire_lock(cfl, 1)) {
+			spin_unlock(&ctx->flc_lock);
+			ret = cfl->fl_lmops->lm_expire_lock(cfl, 0);
+			spin_lock(&ctx->flc_lock);
+			if (ret)
+				goto retry;
 		}
+		locks_copy_conflock(fl, cfl);
+		goto out;
 	}
 	fl->fl_type = F_UNLCK;
 out:
@@ -1140,6 +1150,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 	int error;
 	bool added = false;
 	LIST_HEAD(dispose);
+	bool ret;
 
 	ctx = locks_get_lock_context(inode, request->fl_type);
 	if (!ctx)
@@ -1166,9 +1177,18 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 	 * blocker's list of waiters and the global blocked_hash.
 	 */
 	if (request->fl_type != F_UNLCK) {
+retry:
 		list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
 			if (!posix_locks_conflict(request, fl))
 				continue;
+			if (fl->fl_lmops && fl->fl_lmops->lm_expire_lock &&
+					fl->fl_lmops->lm_expire_lock(fl, 1)) {
+				spin_unlock(&ctx->flc_lock);
+				ret = fl->fl_lmops->lm_expire_lock(fl, 0);
+				spin_lock(&ctx->flc_lock);
+				if (ret)
+					goto retry;
+			}
 			if (conflock)
 				locks_copy_conflock(conflock, fl);
 			error = -EAGAIN;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e7a633353fd2..1a76b6451398 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1071,6 +1071,7 @@ struct lock_manager_operations {
 	int (*lm_change)(struct file_lock *, int, struct list_head *);
 	void (*lm_setup)(struct file_lock *, void **);
 	bool (*lm_breaker_owns_lease)(struct file_lock *);
+	bool (*lm_expire_lock)(struct file_lock *fl, bool testonly);
 };
 
 struct lock_manager {
-- 
2.9.5

[PATCH RFC v4 2/2] nfsd: Initial implementation of NFSv4 Courteous Server

[Dai Ngo]

Currently an NFSv4 client must maintain its lease by using the at least
one of the state tokens or if nothing else, by issuing a RENEW (4.0), or
a singleton SEQUENCE (4.1) at least once during each lease period. If the
client fails to renew the lease, for any reason, the Linux server expunges
the state tokens immediately upon detection of the "failure to renew the
lease" condition and begins returning NFS4ERR_EXPIRED if the client should
reconnect and attempt to use the (now) expired state.

The default lease period for the Linux server is 90 seconds.  The typical
client cuts that in half and will issue a lease renewing operation every
45 seconds. The 90 second lease period is very short considering the
potential for moderately long term network partitions.  A network partition
refers to any loss of network connectivity between the NFS client and the
NFS server, regardless of its root cause.  This includes NIC failures, NIC
driver bugs, network misconfigurations & administrative errors, routers &
switches crashing and/or having software updates applied, even down to
cables being physically pulled.  In most cases, these network failures are
transient, although the duration is unknown.

A server which does not immediately expunge the state on lease expiration
is known as a Courteous Server.  A Courteous Server continues to recognize
previously generated state tokens as valid until conflict arises between
the expired state and the requests from another client, or the server
reboots.

The initial implementation of the Courteous Server will do the following:

. when the laundromat thread detects an expired client and if that client
still has established states on the Linux server and there is no waiters
for the client's locks then mark the client as a COURTESY_CLIENT and skip
destroying the client and all its states, otherwise destroy the client as
usual.

. detects conflict of OPEN request with COURTESY_CLIENT, destroys the
expired client and all its states, skips the delegation recall then allows
the conflicting request to succeed.

. detects conflict of LOCK/LOCKT, NLM LOCK and TEST, and local locks
requests with COURTESY_CLIENT, destroys the expired client and all its
states then allows the conflicting request to succeed.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
 fs/nfsd/nfs4state.c | 269 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 fs/nfsd/state.h     |   3 +
 2 files changed, 269 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 3f4027a5de88..f6d835d6e99b 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -125,6 +125,11 @@ static void free_session(struct nfsd4_session *);
 static const struct nfsd4_callback_ops nfsd4_cb_recall_ops;
 static const struct nfsd4_callback_ops nfsd4_cb_notify_lock_ops;
 
+static struct workqueue_struct *laundry_wq;
+static void laundromat_main(struct work_struct *);
+
+static int courtesy_client_expiry = (24 * 60 * 60);	/* in secs */
+
 static bool is_session_dead(struct nfsd4_session *ses)
 {
 	return ses->se_flags & NFS4_SESSION_DEAD;
@@ -172,6 +177,7 @@ renew_client_locked(struct nfs4_client *clp)
 
 	list_move_tail(&clp->cl_lru, &nn->client_lru);
 	clp->cl_time = ktime_get_boottime_seconds();
+	clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
 }
 
 static void put_client_renew_locked(struct nfs4_client *clp)
@@ -2389,6 +2395,10 @@ static int client_info_show(struct seq_file *m, void *v)
 		seq_puts(m, "status: confirmed\n");
 	else
 		seq_puts(m, "status: unconfirmed\n");
+	seq_printf(m, "courtesy client: %s\n",
+		test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags) ? "yes" : "no");
+	seq_printf(m, "seconds from last renew: %lld\n",
+		ktime_get_boottime_seconds() - clp->cl_time);
 	seq_printf(m, "name: ");
 	seq_quote_mem(m, clp->cl_name.data, clp->cl_name.len);
 	seq_printf(m, "\nminor version: %d\n", clp->cl_minorversion);
@@ -4662,6 +4672,33 @@ static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
 	nfsd4_run_cb(&dp->dl_recall);
 }
 
+/*
+ * This function is called when a file is opened and there is a
+ * delegation conflict with another client. If the other client
+ * is a courtesy client then kick start the laundromat to destroy
+ * it.
+ */
+static bool
+nfsd_check_courtesy_client(struct nfs4_delegation *dp)
+{
+	struct svc_rqst *rqst;
+	struct nfs4_client *clp = dp->dl_recall.cb_clp;
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
+
+	if (!i_am_nfsd())
+		goto out;
+	rqst = kthread_data(current);
+	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
+		return false;
+out:
+	if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
+		set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags);
+		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
+		return true;
+	}
+	return false;
+}
+
 /* Called from break_lease() with i_lock held. */
 static bool
 nfsd_break_deleg_cb(struct file_lock *fl)
@@ -4670,6 +4707,8 @@ nfsd_break_deleg_cb(struct file_lock *fl)
 	struct nfs4_delegation *dp = (struct nfs4_delegation *)fl->fl_owner;
 	struct nfs4_file *fp = dp->dl_stid.sc_file;
 
+	if (nfsd_check_courtesy_client(dp))
+		return false;
 	trace_nfsd_cb_recall(&dp->dl_stid);
 
 	/*
@@ -4912,6 +4951,104 @@ nfsd4_truncate(struct svc_rqst *rqstp, struct svc_fh *fh,
 	return nfsd_setattr(rqstp, fh, &iattr, 0, (time64_t)0);
 }
 
+static bool
+__nfs4_check_deny_bmap(struct nfs4_file *fp, struct nfs4_ol_stateid *stp,
+			u32 access, bool share_access)
+{
+	if (share_access) {
+		if (!stp->st_deny_bmap)
+			return false;
+
+		if ((stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_BOTH)) ||
+			(access & NFS4_SHARE_ACCESS_READ &&
+				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_READ)) ||
+			(access & NFS4_SHARE_ACCESS_WRITE &&
+				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_WRITE))) {
+			return true;
+		}
+		return false;
+	}
+	if ((access & NFS4_SHARE_DENY_BOTH) ||
+		(access & NFS4_SHARE_DENY_READ &&
+			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_READ)) ||
+		(access & NFS4_SHARE_DENY_WRITE &&
+			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_WRITE))) {
+		return true;
+	}
+	return false;
+}
+
+/*
+ * access: access mode if share_access is true else is deny mode
+ */
+static bool
+nfs4_check_deny_bmap(struct nfs4_client *clp, struct nfs4_file *fp,
+				u32 access, bool share_access)
+{
+	int i;
+	struct nfs4_openowner *oo;
+	struct nfs4_stateowner *so, *tmp;
+	struct nfs4_ol_stateid *stp, *stmp;
+
+	spin_lock(&clp->cl_lock);
+	for (i = 0; i < OWNER_HASH_SIZE; i++) {
+		list_for_each_entry_safe(so, tmp, &clp->cl_ownerstr_hashtbl[i],
+					so_strhash) {
+			if (!so->so_is_open_owner)
+				continue;
+			oo = openowner(so);
+			list_for_each_entry_safe(stp, stmp,
+				&oo->oo_owner.so_stateids, st_perstateowner) {
+				if (__nfs4_check_deny_bmap(fp, stp, access,
+						share_access)) {
+					spin_unlock(&clp->cl_lock);
+					return true;
+				}
+			}
+		}
+	}
+	spin_unlock(&clp->cl_lock);
+	return false;
+}
+
+static int
+nfs4_destroy_clnts_with_sresv_conflict(struct svc_rqst *rqstp,
+			struct nfs4_client *clp, struct nfs4_file *fp,
+			u32 access, bool share_access)
+{
+	int cnt = 0;
+	struct nfs4_client *cl;
+	struct list_head *pos, *next, reaplist;
+	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
+
+	INIT_LIST_HEAD(&reaplist);
+	spin_lock(&nn->client_lock);
+	list_for_each_safe(pos, next, &nn->client_lru) {
+		cl = list_entry(pos, struct nfs4_client, cl_lru);
+		if (cl == clp ||
+			(!test_bit(NFSD4_COURTESY_CLIENT, &cl->cl_flags) &&
+			!test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &cl->cl_flags)))
+			continue;
+		/*
+		 * check CS client for deny_bmap that
+		 * matches nfs4_file and access mode
+		 */
+		if (nfs4_check_deny_bmap(cl, fp, access, share_access)) {
+			if (mark_client_expired_locked(cl))
+				continue;
+			list_add(&cl->cl_lru, &reaplist);
+		}
+	}
+	spin_unlock(&nn->client_lock);
+	list_for_each_safe(pos, next, &reaplist) {
+		cl = list_entry(pos, struct nfs4_client, cl_lru);
+		list_del_init(&cl->cl_lru);
+		expire_client(cl);
+		cnt++;
+	}
+	return cnt;
+}
+
 static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
 		struct svc_fh *cur_fh, struct nfs4_ol_stateid *stp,
 		struct nfsd4_open *open)
@@ -4921,6 +5058,7 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
 	int oflag = nfs4_access_to_omode(open->op_share_access);
 	int access = nfs4_access_to_access(open->op_share_access);
 	unsigned char old_access_bmap, old_deny_bmap;
+	int cnt = 0;
 
 	spin_lock(&fp->fi_lock);
 
@@ -4928,16 +5066,46 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
 	 * Are we trying to set a deny mode that would conflict with
 	 * current access?
 	 */
+chk_deny:
 	status = nfs4_file_check_deny(fp, open->op_share_deny);
 	if (status != nfs_ok) {
 		spin_unlock(&fp->fi_lock);
+		if (status != nfserr_share_denied)
+			goto out;
+		/*
+		 * search and destroy all courtesy clients that own
+		 * openstate of nfs4_file, fp, that has st_access_bmap
+		 * that matches open->op_share_deny
+		 */
+		cnt = nfs4_destroy_clnts_with_sresv_conflict(rqstp,
+				stp->st_stateowner->so_client, fp,
+				open->op_share_deny, false);
+		if (cnt) {
+			spin_lock(&fp->fi_lock);
+			goto chk_deny;
+		}
 		goto out;
 	}
 
 	/* set access to the file */
+get_access:
 	status = nfs4_file_get_access(fp, open->op_share_access);
 	if (status != nfs_ok) {
 		spin_unlock(&fp->fi_lock);
+		if (status != nfserr_share_denied)
+			goto out;
+		/*
+		 * search and destroy all courtesy clients that own
+		 * openstate of nfs4_file, fp, that has st_deny_bmap
+		 * that matches open->op_share_access.
+		 */
+		cnt = nfs4_destroy_clnts_with_sresv_conflict(rqstp,
+				stp->st_stateowner->so_client, fp,
+				open->op_share_access, true);
+		if (cnt) {
+			spin_lock(&fp->fi_lock);
+			goto get_access;
+		}
 		goto out;
 	}
 
@@ -5289,6 +5457,22 @@ static void nfsd4_deleg_xgrade_none_ext(struct nfsd4_open *open,
 	 */
 }
 
+static bool
+nfs4_destroy_courtesy_client(struct nfs4_client *clp)
+{
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
+
+	spin_lock(&nn->client_lock);
+	if (!test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags) ||
+			mark_client_expired_locked(clp)) {
+		spin_unlock(&nn->client_lock);
+		return false;
+	}
+	spin_unlock(&nn->client_lock);
+	expire_client(clp);
+	return true;
+}
+
 __be32
 nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nfsd4_open *open)
 {
@@ -5572,6 +5756,47 @@ static void nfsd4_ssc_expire_umount(struct nfsd_net *nn)
 }
 #endif
 
+static
+bool nfs4_anylock_conflict(struct nfs4_client *clp)
+{
+	int i;
+	struct nfs4_stateowner *so, *tmp;
+	struct nfs4_lockowner *lo;
+	struct nfs4_ol_stateid *stp;
+	struct nfs4_file *nf;
+	struct inode *ino;
+	struct file_lock_context *ctx;
+	struct file_lock *fl;
+
+	for (i = 0; i < OWNER_HASH_SIZE; i++) {
+		/* scan each lock owner */
+		list_for_each_entry_safe(so, tmp, &clp->cl_ownerstr_hashtbl[i],
+				so_strhash) {
+			if (so->so_is_open_owner)
+				continue;
+
+			/* scan lock states of this lock owner */
+			lo = lockowner(so);
+			list_for_each_entry(stp, &lo->lo_owner.so_stateids,
+					st_perstateowner) {
+				nf = stp->st_stid.sc_file;
+				ino = nf->fi_inode;
+				ctx = ino->i_flctx;
+				if (!ctx)
+					continue;
+				/* check each lock belongs to this lock state */
+				list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
+					if (fl->fl_owner != lo)
+						continue;
+					if (!list_empty(&fl->fl_blocked_requests))
+						return true;
+				}
+			}
+		}
+	}
+	return false;
+}
+
 static time64_t
 nfs4_laundromat(struct nfsd_net *nn)
 {
@@ -5587,7 +5812,9 @@ nfs4_laundromat(struct nfsd_net *nn)
 	};
 	struct nfs4_cpntf_state *cps;
 	copy_stateid_t *cps_t;
+	struct nfs4_stid *stid;
 	int i;
+	int id = 0;
 
 	if (clients_still_reclaiming(nn)) {
 		lt.new_timeo = 0;
@@ -5608,8 +5835,33 @@ nfs4_laundromat(struct nfsd_net *nn)
 	spin_lock(&nn->client_lock);
 	list_for_each_safe(pos, next, &nn->client_lru) {
 		clp = list_entry(pos, struct nfs4_client, cl_lru);
+		if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags)) {
+			clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
+			goto exp_client;
+		}
+		if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
+			if (ktime_get_boottime_seconds() >= clp->courtesy_client_expiry)
+				goto exp_client;
+			/*
+			 * after umount, v4.0 client is still
+			 * around waiting to be expired
+			 */
+			if (clp->cl_minorversion)
+				continue;
+		}
 		if (!state_expired(&lt, clp->cl_time))
 			break;
+		spin_lock(&clp->cl_lock);
+		stid = idr_get_next(&clp->cl_stateids, &id);
+		spin_unlock(&clp->cl_lock);
+		if (stid && !nfs4_anylock_conflict(clp)) {
+			/* client still has states */
+			clp->courtesy_client_expiry =
+				ktime_get_boottime_seconds() + courtesy_client_expiry;
+			set_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
+			continue;
+		}
+exp_client:
 		if (mark_client_expired_locked(clp))
 			continue;
 		list_add(&clp->cl_lru, &reaplist);
@@ -5689,9 +5941,6 @@ nfs4_laundromat(struct nfsd_net *nn)
 	return max_t(time64_t, lt.new_timeo, NFSD_LAUNDROMAT_MINTIMEOUT);
 }
 
-static struct workqueue_struct *laundry_wq;
-static void laundromat_main(struct work_struct *);
-
 static void
 laundromat_main(struct work_struct *laundry)
 {
@@ -6496,6 +6745,19 @@ nfs4_transform_lock_offset(struct file_lock *lock)
 		lock->fl_end = OFFSET_MAX;
 }
 
+/* return true if lock was expired else return false */
+static bool
+nfsd4_fl_expire_lock(struct file_lock *fl, bool testonly)
+{
+	struct nfs4_lockowner *lo = (struct nfs4_lockowner *)fl->fl_owner;
+	struct nfs4_client *clp = lo->lo_owner.so_client;
+
+	if (testonly)
+		return test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags) ?
+			true : false;
+	return nfs4_destroy_courtesy_client(clp);
+}
+
 static fl_owner_t
 nfsd4_fl_get_owner(fl_owner_t owner)
 {
@@ -6543,6 +6805,7 @@ static const struct lock_manager_operations nfsd_posix_mng_ops  = {
 	.lm_notify = nfsd4_lm_notify,
 	.lm_get_owner = nfsd4_fl_get_owner,
 	.lm_put_owner = nfsd4_fl_put_owner,
+	.lm_expire_lock = nfsd4_fl_expire_lock,
 };
 
 static inline void
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index e73bdbb1634a..93e30b101578 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -345,6 +345,8 @@ struct nfs4_client {
 #define NFSD4_CLIENT_UPCALL_LOCK	(5)	/* upcall serialization */
 #define NFSD4_CLIENT_CB_FLAG_MASK	(1 << NFSD4_CLIENT_CB_UPDATE | \
 					 1 << NFSD4_CLIENT_CB_KILL)
+#define NFSD4_COURTESY_CLIENT		(6)	/* be nice to expired client */
+#define NFSD4_DESTROY_COURTESY_CLIENT	(7)
 	unsigned long		cl_flags;
 	const struct cred	*cl_cb_cred;
 	struct rpc_clnt		*cl_cb_client;
@@ -385,6 +387,7 @@ struct nfs4_client {
 	struct list_head	async_copies;	/* list of async copies */
 	spinlock_t		async_lock;	/* lock for async copies */
 	atomic_t		cl_cb_inflight;	/* Outstanding callbacks */
+	int			courtesy_client_expiry;
 };
 
 /* struct nfs4_client_reset
-- 
2.9.5

Re: [PATCH RFC v4 0/2] nfsd: Initial implementation of NFSv4 Courteous Server

[J. Bruce Fields]

The file_rwsem is used for /proc/locks; only the code that produces the
/proc/locks output calls down_write, the rest only calls down_read.

I assumed that it was OK to nest read acquisitions of a rwsem, but I
think that's wrong.

I think it should be no big deal to move the lm_expire_lock(.,0) call
outside of the file_rwsem?

--b.

[  959.807364] ============================================
[  959.807803] WARNING: possible recursive locking detected
[  959.808228] 5.15.0-rc2-00009-g4e5af4d2635a #533 Not tainted
[  959.808675] --------------------------------------------
[  959.809189] nfsd/5675 is trying to acquire lock:
[  959.809664] ffffffff8519e470 (file_rwsem){.+.+}-{0:0}, at: locks_remove_posix+0x37f/0x4e0
[  959.810647] 
               but task is already holding lock:
[  959.811097] ffffffff8519e470 (file_rwsem){.+.+}-{0:0}, at: nfsd4_lock+0xcb9/0x3850 [nfsd]
[  959.812147] 
               other info that might help us debug this:
[  959.812698]  Possible unsafe locking scenario:

[  959.813189]        CPU0
[  959.813362]        ----
[  959.813544]   lock(file_rwsem);
[  959.813812]   lock(file_rwsem);
[  959.814078] 
                *** DEADLOCK ***

[  959.814386]  May be due to missing lock nesting notation

[  959.814968] 3 locks held by nfsd/5675:
[  959.815315]  #0: ffff888007d42bc8 (&rp->rp_mutex){+.+.}-{3:3}, at: nfs4_preprocess_seqid_op+0x395/0x730 [nfsd]
[  959.816546]  #1: ffff88800f378b70 (&stp->st_mutex#2){+.+.}-{3:3}, at: nfsd4_lock+0x1f91/0x3850 [nfsd]
[  959.817697]  #2: ffffffff8519e470 (file_rwsem){.+.+}-{0:0}, at: nfsd4_lock+0xcb9/0x3850 [nfsd]
[  959.818755] 
               stack backtrace:
[  959.819010] CPU: 2 PID: 5675 Comm: nfsd Not tainted 5.15.0-rc2-00009-g4e5af4d2635a #533
[  959.819847] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-3.fc34 04/01/2014
[  959.820637] Call Trace:
[  959.820759]  dump_stack_lvl+0x45/0x59
[  959.821016]  __lock_acquire.cold+0x175/0x3a5
[  959.821316]  ? lockdep_hardirqs_on_prepare+0x400/0x400
[  959.821741]  lock_acquire+0x1a6/0x4b0
[  959.821976]  ? locks_remove_posix+0x37f/0x4e0
[  959.822316]  ? lock_release+0x6d0/0x6d0
[  959.822591]  ? find_held_lock+0x2c/0x110
[  959.822852]  ? lock_is_held_type+0xd5/0x130
[  959.823139]  posix_lock_inode+0x143/0x1ab0
[  959.823414]  ? locks_remove_posix+0x37f/0x4e0
[  959.823739]  ? do_raw_spin_unlock+0x54/0x220
[  959.824031]  ? lockdep_init_map_type+0x2c3/0x7a0
[  959.824355]  ? locks_remove_flock+0x2e0/0x2e0
[  959.824681]  locks_remove_posix+0x37f/0x4e0
[  959.824984]  ? do_lock_file_wait+0x2a0/0x2a0
[  959.825287]  ? lock_downgrade+0x6a0/0x6a0
[  959.825584]  ? nfsd_file_put+0x170/0x170 [nfsd]
[  959.825941]  filp_close+0xed/0x130
[  959.826191]  nfs4_free_lock_stateid+0xcc/0x190 [nfsd]
[  959.826625]  free_ol_stateid_reaplist+0x128/0x1f0 [nfsd]
[  959.827037]  release_openowner+0xee/0x150 [nfsd]
[  959.827382]  ? release_last_closed_stateid+0x460/0x460 [nfsd]
[  959.827837]  ? rwlock_bug.part.0+0x90/0x90
[  959.828115]  __destroy_client+0x39f/0x6f0 [nfsd]
[  959.828460]  ? nfsd4_cb_recall_release+0x20/0x20 [nfsd]
[  959.828868]  nfsd4_fl_expire_lock+0x2bc/0x460 [nfsd]
[  959.829273]  posix_lock_inode+0xa46/0x1ab0
[  959.829579]  ? lockdep_init_map_type+0x2c3/0x7a0
[  959.829913]  ? locks_remove_flock+0x2e0/0x2e0
[  959.830250]  ? __init_waitqueue_head+0x70/0xd0
[  959.830568]  nfsd4_lock+0xcb9/0x3850 [nfsd]
[  959.830878]  ? nfsd4_delegreturn+0x3b0/0x3b0 [nfsd]
[  959.831248]  ? percpu_counter_add_batch+0x77/0x130
[  959.831594]  nfsd4_proc_compound+0xcee/0x21d0 [nfsd]
[  959.831973]  ? nfsd4_release_compoundargs+0x140/0x140 [nfsd]
[  959.832414]  nfsd_dispatch+0x4df/0xc50 [nfsd]
[  959.832737]  ? nfsd_svc+0xca0/0xca0 [nfsd]
[  959.833051]  svc_process_common+0xdeb/0x2480 [sunrpc]
[  959.833462]  ? svc_create+0x20/0x20 [sunrpc]
[  959.833830]  ? nfsd_svc+0xca0/0xca0 [nfsd]
[  959.834144]  ? svc_sock_secure_port+0x36/0x40 [sunrpc]
[  959.834578]  ? svc_recv+0xd9c/0x2490 [sunrpc]
[  959.834915]  svc_process+0x32e/0x4a0 [sunrpc]
[  959.835249]  nfsd+0x306/0x530 [nfsd]
[  959.835499]  ? nfsd_shutdown_threads+0x300/0x300 [nfsd]
[  959.835899]  kthread+0x391/0x470
[  959.836094]  ? _raw_spin_unlock_irq+0x24/0x50
[  959.836394]  ? set_kthread_struct+0x100/0x100
[  959.836698]  ret_from_fork+0x22/0x30
[  960.750222] nfsd: last server has exited, flushing export cache
[  960.880355] NFSD: Using nfsdcld client tracking operations.
[  960.880956] NFSD: starting 15-second grace period (net f0000098)
[ 1403.405511] nfsd: last server has exited, flushing export cache
[ 1403.656335] NFSD: Using nfsdcld client tracking operations.
[ 1403.657585] NFSD: starting 15-second grace period (net f0000098)
[ 1445.741596] nfsd: last server has exited, flushing export cache
[ 1445.981980] NFSD: Using nfsdcld client tracking operations.
[ 1445.983143] NFSD: starting 15-second grace period (net f0000098)
[ 1450.025112] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
[ 1472.325551] nfsd: last server has exited, flushing export cache
[ 1472.583073] NFSD: Using nfsdcld client tracking operations.
[ 1472.583998] NFSD: starting 15-second grace period (net f0000098)
[ 1473.175582] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
[ 1494.637499] nfsd: last server has exited, flushing export cache
[ 1494.885795] NFSD: Using nfsdcld client tracking operations.
[ 1494.886484] NFSD: starting 15-second grace period (net f0000098)
[ 1495.393667] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
[ 1516.781474] nfsd: last server has exited, flushing export cache
[ 1516.902903] NFSD: Using nfsdcld client tracking operations.
[ 1516.903460] NFSD: starting 15-second grace period (net f0000098)
[ 1538.045156] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
[ 1559.125362] nfsd: last server has exited, flushing export cache
[ 1559.362856] NFSD: Using nfsdcld client tracking operations.
[ 1559.363658] NFSD: starting 15-second grace period (net f0000098)
[ 1559.480531] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
[ 1583.745353] nfsd: last server has exited, flushing export cache
[ 1583.876877] NFSD: Using nfsdcld client tracking operations.
[ 1583.877573] NFSD: starting 15-second grace period (net f0000098)
[ 1586.401321] nfsd: last server has exited, flushing export cache
[ 1586.525629] NFSD: Using nfsdcld client tracking operations.
[ 1586.526388] NFSD: starting 15-second grace period (net f0000098)
[ 1625.993218] nfsd: last server has exited, flushing export cache
[ 1626.442627] NFSD: Using nfsdcld client tracking operations.
[ 1626.444397] NFSD: starting 15-second grace period (net f0000098)
[ 1627.117214] nfsd: last server has exited, flushing export cache
[ 1627.351487] NFSD: Using nfsdcld client tracking operations.
[ 1627.352663] NFSD: starting 15-second grace period (net f0000098)
[ 1627.854410] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
[ 3285.818905] clocksource: timekeeping watchdog on CPU3: acpi_pm retried 2 times before success

Re: [PATCH RFC v4 0/2] nfsd: Initial implementation of NFSv4 Courteous Server

[J. Bruce Fields]

On Mon, Sep 27, 2021 at 04:14:33PM -0400, J. Bruce Fields wrote:
> The file_rwsem is used for /proc/locks; only the code that produces the
> /proc/locks output calls down_write, the rest only calls down_read.
> 
> I assumed that it was OK to nest read acquisitions of a rwsem, but I
> think that's wrong.
> 
> I think it should be no big deal to move the lm_expire_lock(.,0) call
> outside of the file_rwsem?

You probably want to turn on LOCKDEP for any more testing.

I wonder if there's any potential issue with the other locks held here
(st_mutex, rp_mutex).

--b.

> 
> --b.
> 
> [  959.807364] ============================================
> [  959.807803] WARNING: possible recursive locking detected
> [  959.808228] 5.15.0-rc2-00009-g4e5af4d2635a #533 Not tainted
> [  959.808675] --------------------------------------------
> [  959.809189] nfsd/5675 is trying to acquire lock:
> [  959.809664] ffffffff8519e470 (file_rwsem){.+.+}-{0:0}, at: locks_remove_posix+0x37f/0x4e0
> [  959.810647] 
>                but task is already holding lock:
> [  959.811097] ffffffff8519e470 (file_rwsem){.+.+}-{0:0}, at: nfsd4_lock+0xcb9/0x3850 [nfsd]
> [  959.812147] 
>                other info that might help us debug this:
> [  959.812698]  Possible unsafe locking scenario:
> 
> [  959.813189]        CPU0
> [  959.813362]        ----
> [  959.813544]   lock(file_rwsem);
> [  959.813812]   lock(file_rwsem);
> [  959.814078] 
>                 *** DEADLOCK ***
> 
> [  959.814386]  May be due to missing lock nesting notation
> 
> [  959.814968] 3 locks held by nfsd/5675:
> [  959.815315]  #0: ffff888007d42bc8 (&rp->rp_mutex){+.+.}-{3:3}, at: nfs4_preprocess_seqid_op+0x395/0x730 [nfsd]
> [  959.816546]  #1: ffff88800f378b70 (&stp->st_mutex#2){+.+.}-{3:3}, at: nfsd4_lock+0x1f91/0x3850 [nfsd]
> [  959.817697]  #2: ffffffff8519e470 (file_rwsem){.+.+}-{0:0}, at: nfsd4_lock+0xcb9/0x3850 [nfsd]
> [  959.818755] 
>                stack backtrace:
> [  959.819010] CPU: 2 PID: 5675 Comm: nfsd Not tainted 5.15.0-rc2-00009-g4e5af4d2635a #533
> [  959.819847] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-3.fc34 04/01/2014
> [  959.820637] Call Trace:
> [  959.820759]  dump_stack_lvl+0x45/0x59
> [  959.821016]  __lock_acquire.cold+0x175/0x3a5
> [  959.821316]  ? lockdep_hardirqs_on_prepare+0x400/0x400
> [  959.821741]  lock_acquire+0x1a6/0x4b0
> [  959.821976]  ? locks_remove_posix+0x37f/0x4e0
> [  959.822316]  ? lock_release+0x6d0/0x6d0
> [  959.822591]  ? find_held_lock+0x2c/0x110
> [  959.822852]  ? lock_is_held_type+0xd5/0x130
> [  959.823139]  posix_lock_inode+0x143/0x1ab0
> [  959.823414]  ? locks_remove_posix+0x37f/0x4e0
> [  959.823739]  ? do_raw_spin_unlock+0x54/0x220
> [  959.824031]  ? lockdep_init_map_type+0x2c3/0x7a0
> [  959.824355]  ? locks_remove_flock+0x2e0/0x2e0
> [  959.824681]  locks_remove_posix+0x37f/0x4e0
> [  959.824984]  ? do_lock_file_wait+0x2a0/0x2a0
> [  959.825287]  ? lock_downgrade+0x6a0/0x6a0
> [  959.825584]  ? nfsd_file_put+0x170/0x170 [nfsd]
> [  959.825941]  filp_close+0xed/0x130
> [  959.826191]  nfs4_free_lock_stateid+0xcc/0x190 [nfsd]
> [  959.826625]  free_ol_stateid_reaplist+0x128/0x1f0 [nfsd]
> [  959.827037]  release_openowner+0xee/0x150 [nfsd]
> [  959.827382]  ? release_last_closed_stateid+0x460/0x460 [nfsd]
> [  959.827837]  ? rwlock_bug.part.0+0x90/0x90
> [  959.828115]  __destroy_client+0x39f/0x6f0 [nfsd]
> [  959.828460]  ? nfsd4_cb_recall_release+0x20/0x20 [nfsd]
> [  959.828868]  nfsd4_fl_expire_lock+0x2bc/0x460 [nfsd]
> [  959.829273]  posix_lock_inode+0xa46/0x1ab0
> [  959.829579]  ? lockdep_init_map_type+0x2c3/0x7a0
> [  959.829913]  ? locks_remove_flock+0x2e0/0x2e0
> [  959.830250]  ? __init_waitqueue_head+0x70/0xd0
> [  959.830568]  nfsd4_lock+0xcb9/0x3850 [nfsd]
> [  959.830878]  ? nfsd4_delegreturn+0x3b0/0x3b0 [nfsd]
> [  959.831248]  ? percpu_counter_add_batch+0x77/0x130
> [  959.831594]  nfsd4_proc_compound+0xcee/0x21d0 [nfsd]
> [  959.831973]  ? nfsd4_release_compoundargs+0x140/0x140 [nfsd]
> [  959.832414]  nfsd_dispatch+0x4df/0xc50 [nfsd]
> [  959.832737]  ? nfsd_svc+0xca0/0xca0 [nfsd]
> [  959.833051]  svc_process_common+0xdeb/0x2480 [sunrpc]
> [  959.833462]  ? svc_create+0x20/0x20 [sunrpc]
> [  959.833830]  ? nfsd_svc+0xca0/0xca0 [nfsd]
> [  959.834144]  ? svc_sock_secure_port+0x36/0x40 [sunrpc]
> [  959.834578]  ? svc_recv+0xd9c/0x2490 [sunrpc]
> [  959.834915]  svc_process+0x32e/0x4a0 [sunrpc]
> [  959.835249]  nfsd+0x306/0x530 [nfsd]
> [  959.835499]  ? nfsd_shutdown_threads+0x300/0x300 [nfsd]
> [  959.835899]  kthread+0x391/0x470
> [  959.836094]  ? _raw_spin_unlock_irq+0x24/0x50
> [  959.836394]  ? set_kthread_struct+0x100/0x100
> [  959.836698]  ret_from_fork+0x22/0x30
> [  960.750222] nfsd: last server has exited, flushing export cache
> [  960.880355] NFSD: Using nfsdcld client tracking operations.
> [  960.880956] NFSD: starting 15-second grace period (net f0000098)
> [ 1403.405511] nfsd: last server has exited, flushing export cache
> [ 1403.656335] NFSD: Using nfsdcld client tracking operations.
> [ 1403.657585] NFSD: starting 15-second grace period (net f0000098)
> [ 1445.741596] nfsd: last server has exited, flushing export cache
> [ 1445.981980] NFSD: Using nfsdcld client tracking operations.
> [ 1445.983143] NFSD: starting 15-second grace period (net f0000098)
> [ 1450.025112] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
> [ 1472.325551] nfsd: last server has exited, flushing export cache
> [ 1472.583073] NFSD: Using nfsdcld client tracking operations.
> [ 1472.583998] NFSD: starting 15-second grace period (net f0000098)
> [ 1473.175582] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
> [ 1494.637499] nfsd: last server has exited, flushing export cache
> [ 1494.885795] NFSD: Using nfsdcld client tracking operations.
> [ 1494.886484] NFSD: starting 15-second grace period (net f0000098)
> [ 1495.393667] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
> [ 1516.781474] nfsd: last server has exited, flushing export cache
> [ 1516.902903] NFSD: Using nfsdcld client tracking operations.
> [ 1516.903460] NFSD: starting 15-second grace period (net f0000098)
> [ 1538.045156] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
> [ 1559.125362] nfsd: last server has exited, flushing export cache
> [ 1559.362856] NFSD: Using nfsdcld client tracking operations.
> [ 1559.363658] NFSD: starting 15-second grace period (net f0000098)
> [ 1559.480531] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
> [ 1583.745353] nfsd: last server has exited, flushing export cache
> [ 1583.876877] NFSD: Using nfsdcld client tracking operations.
> [ 1583.877573] NFSD: starting 15-second grace period (net f0000098)
> [ 1586.401321] nfsd: last server has exited, flushing export cache
> [ 1586.525629] NFSD: Using nfsdcld client tracking operations.
> [ 1586.526388] NFSD: starting 15-second grace period (net f0000098)
> [ 1625.993218] nfsd: last server has exited, flushing export cache
> [ 1626.442627] NFSD: Using nfsdcld client tracking operations.
> [ 1626.444397] NFSD: starting 15-second grace period (net f0000098)
> [ 1627.117214] nfsd: last server has exited, flushing export cache
> [ 1627.351487] NFSD: Using nfsdcld client tracking operations.
> [ 1627.352663] NFSD: starting 15-second grace period (net f0000098)
> [ 1627.854410] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
> [ 3285.818905] clocksource: timekeeping watchdog on CPU3: acpi_pm retried 2 times before success

Re: [PATCH RFC v4 0/2] nfsd: Initial implementation of NFSv4 Courteous Server

[dai.ngo]

On 9/27/21 1:39 PM, J. Bruce Fields wrote:
> On Mon, Sep 27, 2021 at 04:14:33PM -0400, J. Bruce Fields wrote:
>> The file_rwsem is used for /proc/locks; only the code that produces the
>> /proc/locks output calls down_write, the rest only calls down_read.
>>
>> I assumed that it was OK to nest read acquisitions of a rwsem, but I
>> think that's wrong.
>>
>> I think it should be no big deal to move the lm_expire_lock(.,0) call
>> outside of the file_rwsem?
> You probably want to turn on LOCKDEP for any more testing.

I use 'make menuconfig' to turn on LOCKDEP by enabling
'Kernel hacking/Lock debugging/prove locking correctness'. However
when I boot this kernel, DHCP failed to get an IP address making
the system inaccessible from the network. I'm not sure if it's
related to this error:

Sep 27 23:14:51 nfsvme24 kernel: unchecked MSR access error: WRMSR to 0xe00 (tried to write 0x0000000000010003) at rIP: 0xffffffff8101584d (wrmsrl+0xb/0x1f)
Sep 27 23:14:51 nfsvme24 kernel: Call Trace:
Sep 27 23:14:51 nfsvme24 kernel: uncore_box_ref.part.0+0x60/0x78
Sep 27 23:14:51 nfsvme24 kernel: ? uncore_pci_pmu_register+0xea/0xea
Sep 27 23:14:51 nfsvme24 kernel: uncore_event_cpu_online+0x51/0x107
Sep 27 23:14:51 nfsvme24 kernel: ? uncore_pci_pmu_register+0xea/0xea
Sep 27 23:14:51 nfsvme24 kernel: cpuhp_invoke_callback+0xb2/0x23d
Sep 27 23:14:51 nfsvme24 kernel: ? __schedule+0x5d3/0x625
Sep 27 23:14:51 nfsvme24 kernel: cpuhp_thread_fun+0xc6/0x111
Sep 27 23:14:51 nfsvme24 kernel: ? smpboot_register_percpu_thread+0xcc/0xcc
Sep 27 23:14:51 nfsvme24 kernel: smpboot_thread_fn+0x1b1/0x1c6
Sep 27 23:14:51 nfsvme24 kernel: kthread+0x107/0x10f
Sep 27 23:14:51 nfsvme24 kernel: ? kthread_flush_worker+0x75/0x75
Sep 27 23:14:51 nfsvme24 kernel: ret_from_fork+0x22/0x30

Here is the diff of the working config and non-working (LOCKDEP) config:

[dngo@nfsdev linux]$ diff .config .config-LOCKDEP
245c245
< # CONFIG_KALLSYMS_ALL is not set
---
> CONFIG_KALLSYMS_ALL=y
470a471
> # CONFIG_LIVEPATCH is not set
905,909c906
< CONFIG_INLINE_SPIN_UNLOCK_IRQ=y
< CONFIG_INLINE_READ_UNLOCK=y
< CONFIG_INLINE_READ_UNLOCK_IRQ=y
< CONFIG_INLINE_WRITE_UNLOCK=y
< CONFIG_INLINE_WRITE_UNLOCK_IRQ=y
---
> CONFIG_UNINLINE_SPIN_UNLOCK=y
4463,4470c4460,4475
< # CONFIG_PROVE_LOCKING is not set
< # CONFIG_LOCK_STAT is not set
< # CONFIG_DEBUG_RT_MUTEXES is not set
< # CONFIG_DEBUG_SPINLOCK is not set
< # CONFIG_DEBUG_MUTEXES is not set
< # CONFIG_DEBUG_WW_MUTEX_SLOWPATH is not set
< # CONFIG_DEBUG_RWSEMS is not set
< # CONFIG_DEBUG_LOCK_ALLOC is not set
---
> CONFIG_PROVE_LOCKING=y
> CONFIG_PROVE_RAW_LOCK_NESTING=y
> CONFIG_LOCK_STAT=y
> CONFIG_DEBUG_RT_MUTEXES=y
> CONFIG_DEBUG_SPINLOCK=y
> CONFIG_DEBUG_MUTEXES=y
> CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y
> CONFIG_DEBUG_RWSEMS=y
> CONFIG_DEBUG_LOCK_ALLOC=y
> CONFIG_LOCKDEP=y
> CONFIG_LOCKDEP_BITS=15
> CONFIG_LOCKDEP_CHAINS_BITS=16
> CONFIG_LOCKDEP_STACK_TRACE_BITS=19
> CONFIG_LOCKDEP_STACK_TRACE_HASH_BITS=14
> CONFIG_LOCKDEP_CIRCULAR_QUEUE_BITS=12
> CONFIG_DEBUG_LOCKDEP=y
4479c4484,4486
< # CONFIG_DEBUG_IRQFLAGS is not set
---
> CONFIG_TRACE_IRQFLAGS=y
> CONFIG_TRACE_IRQFLAGS_NMI=y
> CONFIG_DEBUG_IRQFLAGS=y
4498a4506
> CONFIG_PROVE_RCU=y
4526a4535
> CONFIG_PREEMPTIRQ_TRACEPOINTS=y
[dngo@nfsdev linux]$

can you share your config with LOCKDEP enabled so I can give
it a try?

Thanks,
-Dai

>
> I wonder if there's any potential issue with the other locks held here
> (st_mutex, rp_mutex).
>
> --b.
>
>> --b.
>>
>> [  959.807364] ============================================
>> [  959.807803] WARNING: possible recursive locking detected
>> [  959.808228] 5.15.0-rc2-00009-g4e5af4d2635a #533 Not tainted
>> [  959.808675] --------------------------------------------
>> [  959.809189] nfsd/5675 is trying to acquire lock:
>> [  959.809664] ffffffff8519e470 (file_rwsem){.+.+}-{0:0}, at: locks_remove_posix+0x37f/0x4e0
>> [  959.810647]
>>                 but task is already holding lock:
>> [  959.811097] ffffffff8519e470 (file_rwsem){.+.+}-{0:0}, at: nfsd4_lock+0xcb9/0x3850 [nfsd]
>> [  959.812147]
>>                 other info that might help us debug this:
>> [  959.812698]  Possible unsafe locking scenario:
>>
>> [  959.813189]        CPU0
>> [  959.813362]        ----
>> [  959.813544]   lock(file_rwsem);
>> [  959.813812]   lock(file_rwsem);
>> [  959.814078]
>>                  *** DEADLOCK ***
>>
>> [  959.814386]  May be due to missing lock nesting notation
>>
>> [  959.814968] 3 locks held by nfsd/5675:
>> [  959.815315]  #0: ffff888007d42bc8 (&rp->rp_mutex){+.+.}-{3:3}, at: nfs4_preprocess_seqid_op+0x395/0x730 [nfsd]
>> [  959.816546]  #1: ffff88800f378b70 (&stp->st_mutex#2){+.+.}-{3:3}, at: nfsd4_lock+0x1f91/0x3850 [nfsd]
>> [  959.817697]  #2: ffffffff8519e470 (file_rwsem){.+.+}-{0:0}, at: nfsd4_lock+0xcb9/0x3850 [nfsd]
>> [  959.818755]
>>                 stack backtrace:
>> [  959.819010] CPU: 2 PID: 5675 Comm: nfsd Not tainted 5.15.0-rc2-00009-g4e5af4d2635a #533
>> [  959.819847] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-3.fc34 04/01/2014
>> [  959.820637] Call Trace:
>> [  959.820759]  dump_stack_lvl+0x45/0x59
>> [  959.821016]  __lock_acquire.cold+0x175/0x3a5
>> [  959.821316]  ? lockdep_hardirqs_on_prepare+0x400/0x400
>> [  959.821741]  lock_acquire+0x1a6/0x4b0
>> [  959.821976]  ? locks_remove_posix+0x37f/0x4e0
>> [  959.822316]  ? lock_release+0x6d0/0x6d0
>> [  959.822591]  ? find_held_lock+0x2c/0x110
>> [  959.822852]  ? lock_is_held_type+0xd5/0x130
>> [  959.823139]  posix_lock_inode+0x143/0x1ab0
>> [  959.823414]  ? locks_remove_posix+0x37f/0x4e0
>> [  959.823739]  ? do_raw_spin_unlock+0x54/0x220
>> [  959.824031]  ? lockdep_init_map_type+0x2c3/0x7a0
>> [  959.824355]  ? locks_remove_flock+0x2e0/0x2e0
>> [  959.824681]  locks_remove_posix+0x37f/0x4e0
>> [  959.824984]  ? do_lock_file_wait+0x2a0/0x2a0
>> [  959.825287]  ? lock_downgrade+0x6a0/0x6a0
>> [  959.825584]  ? nfsd_file_put+0x170/0x170 [nfsd]
>> [  959.825941]  filp_close+0xed/0x130
>> [  959.826191]  nfs4_free_lock_stateid+0xcc/0x190 [nfsd]
>> [  959.826625]  free_ol_stateid_reaplist+0x128/0x1f0 [nfsd]
>> [  959.827037]  release_openowner+0xee/0x150 [nfsd]
>> [  959.827382]  ? release_last_closed_stateid+0x460/0x460 [nfsd]
>> [  959.827837]  ? rwlock_bug.part.0+0x90/0x90
>> [  959.828115]  __destroy_client+0x39f/0x6f0 [nfsd]
>> [  959.828460]  ? nfsd4_cb_recall_release+0x20/0x20 [nfsd]
>> [  959.828868]  nfsd4_fl_expire_lock+0x2bc/0x460 [nfsd]
>> [  959.829273]  posix_lock_inode+0xa46/0x1ab0
>> [  959.829579]  ? lockdep_init_map_type+0x2c3/0x7a0
>> [  959.829913]  ? locks_remove_flock+0x2e0/0x2e0
>> [  959.830250]  ? __init_waitqueue_head+0x70/0xd0
>> [  959.830568]  nfsd4_lock+0xcb9/0x3850 [nfsd]
>> [  959.830878]  ? nfsd4_delegreturn+0x3b0/0x3b0 [nfsd]
>> [  959.831248]  ? percpu_counter_add_batch+0x77/0x130
>> [  959.831594]  nfsd4_proc_compound+0xcee/0x21d0 [nfsd]
>> [  959.831973]  ? nfsd4_release_compoundargs+0x140/0x140 [nfsd]
>> [  959.832414]  nfsd_dispatch+0x4df/0xc50 [nfsd]
>> [  959.832737]  ? nfsd_svc+0xca0/0xca0 [nfsd]
>> [  959.833051]  svc_process_common+0xdeb/0x2480 [sunrpc]
>> [  959.833462]  ? svc_create+0x20/0x20 [sunrpc]
>> [  959.833830]  ? nfsd_svc+0xca0/0xca0 [nfsd]
>> [  959.834144]  ? svc_sock_secure_port+0x36/0x40 [sunrpc]
>> [  959.834578]  ? svc_recv+0xd9c/0x2490 [sunrpc]
>> [  959.834915]  svc_process+0x32e/0x4a0 [sunrpc]
>> [  959.835249]  nfsd+0x306/0x530 [nfsd]
>> [  959.835499]  ? nfsd_shutdown_threads+0x300/0x300 [nfsd]
>> [  959.835899]  kthread+0x391/0x470
>> [  959.836094]  ? _raw_spin_unlock_irq+0x24/0x50
>> [  959.836394]  ? set_kthread_struct+0x100/0x100
>> [  959.836698]  ret_from_fork+0x22/0x30
>> [  960.750222] nfsd: last server has exited, flushing export cache
>> [  960.880355] NFSD: Using nfsdcld client tracking operations.
>> [  960.880956] NFSD: starting 15-second grace period (net f0000098)
>> [ 1403.405511] nfsd: last server has exited, flushing export cache
>> [ 1403.656335] NFSD: Using nfsdcld client tracking operations.
>> [ 1403.657585] NFSD: starting 15-second grace period (net f0000098)
>> [ 1445.741596] nfsd: last server has exited, flushing export cache
>> [ 1445.981980] NFSD: Using nfsdcld client tracking operations.
>> [ 1445.983143] NFSD: starting 15-second grace period (net f0000098)
>> [ 1450.025112] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
>> [ 1472.325551] nfsd: last server has exited, flushing export cache
>> [ 1472.583073] NFSD: Using nfsdcld client tracking operations.
>> [ 1472.583998] NFSD: starting 15-second grace period (net f0000098)
>> [ 1473.175582] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
>> [ 1494.637499] nfsd: last server has exited, flushing export cache
>> [ 1494.885795] NFSD: Using nfsdcld client tracking operations.
>> [ 1494.886484] NFSD: starting 15-second grace period (net f0000098)
>> [ 1495.393667] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
>> [ 1516.781474] nfsd: last server has exited, flushing export cache
>> [ 1516.902903] NFSD: Using nfsdcld client tracking operations.
>> [ 1516.903460] NFSD: starting 15-second grace period (net f0000098)
>> [ 1538.045156] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
>> [ 1559.125362] nfsd: last server has exited, flushing export cache
>> [ 1559.362856] NFSD: Using nfsdcld client tracking operations.
>> [ 1559.363658] NFSD: starting 15-second grace period (net f0000098)
>> [ 1559.480531] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
>> [ 1583.745353] nfsd: last server has exited, flushing export cache
>> [ 1583.876877] NFSD: Using nfsdcld client tracking operations.
>> [ 1583.877573] NFSD: starting 15-second grace period (net f0000098)
>> [ 1586.401321] nfsd: last server has exited, flushing export cache
>> [ 1586.525629] NFSD: Using nfsdcld client tracking operations.
>> [ 1586.526388] NFSD: starting 15-second grace period (net f0000098)
>> [ 1625.993218] nfsd: last server has exited, flushing export cache
>> [ 1626.442627] NFSD: Using nfsdcld client tracking operations.
>> [ 1626.444397] NFSD: starting 15-second grace period (net f0000098)
>> [ 1627.117214] nfsd: last server has exited, flushing export cache
>> [ 1627.351487] NFSD: Using nfsdcld client tracking operations.
>> [ 1627.352663] NFSD: starting 15-second grace period (net f0000098)
>> [ 1627.854410] NFSD: all clients done reclaiming, ending NFSv4 grace period (net f0000098)
>> [ 3285.818905] clocksource: timekeeping watchdog on CPU3: acpi_pm retried 2 times before success