git: cfd0d2cd2ce1 - stable/15 - nfscl: Fix oddball cases for session slot release

The branch stable/15 has been updated by rmacklem:

URL: https://cgit.FreeBSD.org/src/commit/?id=cfd0d2cd2ce1ab4384863a5c80c4ded33f743c3d

commit cfd0d2cd2ce1ab4384863a5c80c4ded33f743c3d
Author:     J. David <j.david.lists@gmail.com>
AuthorDate: 2026-10-07 01:52:19 +0000
Commit:     Rick Macklem <rmacklem@FreeBSD.org>
CommitDate: 2026-10-14 01:11:51 +0000

    nfscl: Fix oddball cases for session slot release
    
    We have identified some cases where silent slot loss can occur
    when operations on NFS mounts are aborted. We experience this
    when using NFSv4.2, but it likely also occurs with NFSv4.1.
    
    A slot is acquired for compound operations by nfsv4_setsequence()
    and freed by newnfs_request(). Any call path that abandons the
    compound before reaching newnfs_request() loses the slot permanently.
    
    We identified four call sites where this happens, one of
    which where it actually does happen for us in a semi-reproducible
    way, which allowed us to develop a candidate patch, attached.
    
    The patch adds one function, nfsv4_freeunsentslot(), to
    nfs_clcomsubs.c. It is called from each of the four call
    sites: nfsrpc_writerpc(), nfsrpc_writeds(), and two in
    nfsrpc_setextattr().
    
    nfsv4_freeunsentslot() calls nfsv4_freeslot() with resetseq
    set to true because the aborted RPC will never be sent and
    therefore the slot sequence ID should not advance.
    
    With this patch and other diagnostics, we have confirmed
    that slot loss does not occur under the conditions that
    otherwise cause it in our environment.
    
    PR:     298416
    
    (cherry picked from commit 77a7a48a1cb003831ff1d4342b1974fc7f79381e)
---
 sys/fs/nfs/nfs_var.h             |  2 ++
 sys/fs/nfsclient/nfs_clcomsubs.c | 18 ++++++++++++++++++
 sys/fs/nfsclient/nfs_clrpcops.c  |  4 ++++
 3 files changed, 24 insertions(+)

diff --git a/sys/fs/nfs/nfs_var.h b/sys/fs/nfs/nfs_var.h
index 3572cd386707..1bf2c9a91f87 100644
--- a/sys/fs/nfs/nfs_var.h
+++ b/sys/fs/nfs/nfs_var.h
@@ -383,6 +383,8 @@ int nfscl_wcc_data(struct nfsrv_descript *, vnode_t,
 int nfsm_loadattr(struct nfsrv_descript *, struct nfsvattr *);
 int nfscl_request(struct nfsrv_descript *, vnode_t,
          NFSPROC_T *, struct ucred *);
+void nfsv4_freeunsentslot(struct nfsmount *, struct nfsclsession *,
+    struct nfsrv_descript *);
 
 /* nfs_nfsdsubs.c */
 void nfsd_fhtovp(struct nfsrv_descript *, struct nfsrvfh *, int,
diff --git a/sys/fs/nfsclient/nfs_clcomsubs.c b/sys/fs/nfsclient/nfs_clcomsubs.c
index 2b48e257381e..fa814ea0b84d 100644
--- a/sys/fs/nfsclient/nfs_clcomsubs.c
+++ b/sys/fs/nfsclient/nfs_clcomsubs.c
@@ -445,3 +445,21 @@ nfscl_lockderef(struct nfsv4lock *lckp)
 	}
 	NFSUNLOCKCLSTATE();
 }
+
+/*
+ * Free the session slot of a compound that was built but will not be sent
+ * to the server.
+ */
+void
+nfsv4_freeunsentslot(struct nfsmount *nmp, struct nfsclsession *sep,
+    struct nfsrv_descript *nd)
+{
+
+	if (nmp == NULL || (nd->nd_flag & (ND_NFSV41 | ND_HASSLOTID)) !=
+	    (ND_NFSV41 | ND_HASSLOTID))
+		return;
+	if (sep == NULL)
+		sep = nfsmnt_mdssession(nmp);
+	if (sep != NULL)
+		nfsv4_freeslot(sep, nd->nd_slotid, true);
+}
diff --git a/sys/fs/nfsclient/nfs_clrpcops.c b/sys/fs/nfsclient/nfs_clrpcops.c
index dc42170e0577..7afc8ce309c5 100644
--- a/sys/fs/nfsclient/nfs_clrpcops.c
+++ b/sys/fs/nfsclient/nfs_clrpcops.c
@@ -2067,6 +2067,7 @@ nfsrpc_writerpc(vnode_t vp, struct uio *uiop, int *iomode,
 		}
 		error = nfsm_uiombuf(nd, uiop, len);
 		if (error != 0) {
+			nfsv4_freeunsentslot(nmp, NULL, nd);
 			m_freem(nd->nd_mreq);
 			free(nd, M_TEMP);
 			return (error);
@@ -7215,6 +7216,7 @@ nfsrpc_writeds(vnode_t vp, struct uio *uiop, int *iomode, int *must_commit,
 	*tl = txdr_unsigned(len);
 	error = nfsm_uiombuf(nd, uiop, len);
 	if (error != 0) {
+		nfsv4_freeunsentslot(nmp, &dsp->nfsclds_sess, nd);
 		m_freem(nd->nd_mreq);
 		return (error);
 	}
@@ -9556,6 +9558,7 @@ nfsrpc_setextattr(vnode_t vp, const char *name, struct uio *uiop,
 	NFSCL_REQSTART(nd, NFSPROC_SETEXTATTR, vp, cred);
 	if (uiop->uio_resid > nd->nd_maxreq) {
 		/* nd_maxreq is set by NFSCL_REQSTART(). */
+		nfsv4_freeunsentslot(VFSTONFS(vp->v_mount), NULL, nd);
 		m_freem(nd->nd_mreq);
 		return (EINVAL);
 	}
@@ -9566,6 +9569,7 @@ nfsrpc_setextattr(vnode_t vp, const char *name, struct uio *uiop,
 	*tl = txdr_unsigned(uiop->uio_resid);
 	error = nfsm_uiombuf(nd, uiop, uiop->uio_resid);
 	if (error != 0) {
+		nfsv4_freeunsentslot(VFSTONFS(vp->v_mount), NULL, nd);
 		m_freem(nd->nd_mreq);
 		return (error);
 	}