Patch "nfsd: hold a lighter-weight client reference over CB_RECALL_ANY" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    nfsd: hold a lighter-weight client reference over CB_RECALL_ANY

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nfsd-hold-a-lighter-weight-client-reference-over-cb_.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 4422008ec5d7b599e04561afda743969c3b43f05
Author: Jeff Layton <jlayton@xxxxxxxxxx>
Date:   Fri Apr 5 13:56:18 2024 -0400

    nfsd: hold a lighter-weight client reference over CB_RECALL_ANY
    
    [ Upstream commit 10396f4df8b75ff6ab0aa2cd74296565466f2c8d ]
    
    Currently the CB_RECALL_ANY job takes a cl_rpc_users reference to the
    client. While a callback job is technically an RPC that counter is
    really more for client-driven RPCs, and this has the effect of
    preventing the client from being unhashed until the callback completes.
    
    If nfsd decides to send a CB_RECALL_ANY just as the client reboots, we
    can end up in a situation where the callback can't complete on the (now
    dead) callback channel, but the new client can't connect because the old
    client can't be unhashed. This usually manifests as a NFS4ERR_DELAY
    return on the CREATE_SESSION operation.
    
    The job is only holding a reference to the client so it can clear a flag
    after the RPC completes. Fix this by having CB_RECALL_ANY instead hold a
    reference to the cl_nfsdfs.cl_ref. Typically we only take that sort of
    reference when dealing with the nfsdfs info files, but it should work
    appropriately here to ensure that the nfs4_client doesn't disappear.
    
    Fixes: 44df6f439a17 ("NFSD: add delegation reaper to react to low memory condition")
    Reported-by: Vladimir Benes <vbenes@xxxxxxxxxx>
    Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index e4522e86e984e..8d15959004ad2 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -2889,12 +2889,9 @@ static void
 nfsd4_cb_recall_any_release(struct nfsd4_callback *cb)
 {
 	struct nfs4_client *clp = cb->cb_clp;
-	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
 
-	spin_lock(&nn->client_lock);
 	clear_bit(NFSD4_CLIENT_CB_RECALL_ANY, &clp->cl_flags);
-	put_client_renew_locked(clp);
-	spin_unlock(&nn->client_lock);
+	drop_client(clp);
 }
 
 static const struct nfsd4_callback_ops nfsd4_cb_recall_any_ops = {
@@ -6231,7 +6228,7 @@ deleg_reaper(struct nfsd_net *nn)
 		list_add(&clp->cl_ra_cblist, &cblist);
 
 		/* release in nfsd4_cb_recall_any_release */
-		atomic_inc(&clp->cl_rpc_users);
+		kref_get(&clp->cl_nfsdfs.cl_ref);
 		set_bit(NFSD4_CLIENT_CB_RECALL_ANY, &clp->cl_flags);
 		clp->cl_ra_time = ktime_get_boottime_seconds();
 	}




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