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From:   trondmy@kernel.org
To:     Anna Schumaker <anna.schumaker@netapp.com>
Cc:     linux-nfs@vger.kernel.org
Subject: [PATCH 1/3] NFSv4: Fix a potential state reclaim deadlock
Date:   Sun, 16 Oct 2022 14:44:31 -0400
Message-Id: <20221016184433.31213-1-trondmy@kernel.org>
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From: Trond Myklebust <trond.myklebust@hammerspace.com>

If the server reboots while we are engaged in a delegation return, and
there is a pNFS layout with return-on-close set, then the current code
can end up deadlocking in pnfs_roc() when nfs_inode_set_delegation()
tries to return the old delegation.
Now that delegreturn actually uses its own copy of the stateid, it
should be safe to just always update the delegation stateid in place.

Fixes: 078000d02d57 ("pNFS: We want return-on-close to complete when evicting the inode")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/delegation.c | 36 +++++++++++++++++-------------------
 1 file changed, 17 insertions(+), 19 deletions(-)

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 5c97cad741a7..ead8a0e06abf 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -228,8 +228,7 @@ static int nfs_delegation_claim_opens(struct inode *inode,
  *
  */
 void nfs_inode_reclaim_delegation(struct inode *inode, const struct cred *cred,
-				  fmode_t type,
-				  const nfs4_stateid *stateid,
+				  fmode_t type, const nfs4_stateid *stateid,
 				  unsigned long pagemod_limit)
 {
 	struct nfs_delegation *delegation;
@@ -239,25 +238,24 @@ void nfs_inode_reclaim_delegation(struct inode *inode, const struct cred *cred,
 	delegation = rcu_dereference(NFS_I(inode)->delegation);
 	if (delegation != NULL) {
 		spin_lock(&delegation->lock);
-		if (nfs4_is_valid_delegation(delegation, 0)) {
-			nfs4_stateid_copy(&delegation->stateid, stateid);
-			delegation->type = type;
-			delegation->pagemod_limit = pagemod_limit;
-			oldcred = delegation->cred;
-			delegation->cred = get_cred(cred);
-			clear_bit(NFS_DELEGATION_NEED_RECLAIM,
-				  &delegation->flags);
-			spin_unlock(&delegation->lock);
-			rcu_read_unlock();
-			put_cred(oldcred);
-			trace_nfs4_reclaim_delegation(inode, type);
-			return;
-		}
-		/* We appear to have raced with a delegation return. */
+		nfs4_stateid_copy(&delegation->stateid, stateid);
+		delegation->type = type;
+		delegation->pagemod_limit = pagemod_limit;
+		oldcred = delegation->cred;
+		delegation->cred = get_cred(cred);
+		clear_bit(NFS_DELEGATION_NEED_RECLAIM, &delegation->flags);
+		if (test_and_clear_bit(NFS_DELEGATION_REVOKED,
+				       &delegation->flags))
+			atomic_long_inc(&nfs_active_delegations);
 		spin_unlock(&delegation->lock);
+		rcu_read_unlock();
+		put_cred(oldcred);
+		trace_nfs4_reclaim_delegation(inode, type);
+	} else {
+		rcu_read_unlock();
+		nfs_inode_set_delegation(inode, cred, type, stateid,
+					 pagemod_limit);
 	}
-	rcu_read_unlock();
-	nfs_inode_set_delegation(inode, cred, type, stateid, pagemod_limit);
 }
 
 static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *delegation, int issync)
-- 
2.37.3