[PATCH v2 8/8] pnfs/blocklayout: Complete a device upcall when the pipe is closed

[Chuck Lever <cel@kernel.org>]

Once blkmapd has read a whole upcall, rpc_pipe_read() unlinks the
message from every pipe list, so the purges in rpc_pipe_release()
and rpc_close_pipes() no longer reach it. bl_upcall_ops supplies no
.release_pipe callback, and bl_pipe_destroy_msg() returns without
completing the upcall because a downcall is expected to follow. A
daemon that exits between the read and the write therefore strands
its waiter: bl_resolve_deviceid() sleeps in wait_for_completion()
and never returns, and it holds nn->bl_mutex across that wait, so
every later device resolution in the net namespace blocks behind
it.

Add a .release_pipe that completes an upcall blkmapd has consumed
and left unanswered. Completing an upcall retires it, so a message
the framework has already purged is no longer in flight and is not
completed a second time here.

Fixes: fe0a9b740881 ("pnfsblock: add device operations")
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfs/blocklayout/rpc_pipefs.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/fs/nfs/blocklayout/rpc_pipefs.c b/fs/nfs/blocklayout/rpc_pipefs.c
index 50f276a90527..f0004a8249e7 100644
--- a/fs/nfs/blocklayout/rpc_pipefs.c
+++ b/fs/nfs/blocklayout/rpc_pipefs.c
@@ -151,10 +151,31 @@ static void bl_pipe_destroy_msg(struct rpc_pipe_msg *msg)
 	complete(&nn->bl_done);
 }
 
+/*
+ * An upcall blkmapd has consumed is off every pipe list, so the
+ * purges in rpc_pipe_release() and rpc_close_pipes() cannot reach it.
+ * No downcall can arrive once the pipe is closed; release its waiter
+ * here.
+ */
+static void bl_release_pipe(struct inode *inode)
+{
+	struct nfs_net *nn = net_generic(inode->i_sb->s_fs_info, nfs_net_id);
+	struct rpc_pipe *pipe = nn->bl_device_pipe;
+
+	spin_lock(&pipe->lock);
+	if (rpc_msg_is_inflight(&nn->bl_pipe_msg)) {
+		nn->bl_pipe_msg.copied = 0;
+		nn->bl_pipe_msg.errno = -EPIPE;
+		complete(&nn->bl_done);
+	}
+	spin_unlock(&pipe->lock);
+}
+
 static const struct rpc_pipe_ops bl_upcall_ops = {
 	.upcall		= rpc_pipe_generic_upcall,
 	.downcall	= bl_pipe_downcall,
 	.destroy_msg	= bl_pipe_destroy_msg,
+	.release_pipe	= bl_release_pipe,
 };
 
 static int nfs4blocklayout_register_sb(struct super_block *sb,

-- 
2.54.0