From: NeilBrown <neilb@suse.de>
Date: Wed, 27 Oct 2021 15:26:10 +1100
Subject: [PATCH] SUNRPC/call_alloc: async tasks mustn't block waiting for
 memory
Patch-mainline: v5.18
Git-commit: c487216bec83b0c5a8803e5c61433d33ad7b104d
References: bsc#1191876 bsc#1192866

When memory is short, new worker threads cannot be created and we depend
on the minimum one rpciod thread to be able to handle everything.
So it must not block waiting for memory.

mempools are particularly a problem as memory can only be released back
to the mempool by an async rpc task running.  If all available
workqueue threads are waiting on the mempool, no thread is available to
return anything.

rpc_malloc() can block, and this might cause deadlocks.
So check RPC_IS_ASYNC(), rather than RPC_IS_SWAPPER() to determine if
blocking is acceptable.

Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: NeilBrown <neilb@suse.com>

---
 net/sunrpc/sched.c              |    4 +++-
 net/sunrpc/xprtrdma/transport.c |    4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -885,8 +885,10 @@ int rpc_malloc(struct rpc_task *task)
 	struct rpc_buffer *buf;
 	gfp_t gfp = GFP_NOIO | __GFP_NOWARN;
 
+	if (RPC_IS_ASYNC(task))
+		gfp = GFP_NOWAIT | __GFP_NOWARN;
 	if (RPC_IS_SWAPPER(task))
-		gfp = __GFP_MEMALLOC | GFP_NOWAIT | __GFP_NOWARN;
+		gfp |= __GFP_MEMALLOC;
 
 	size += sizeof(struct rpc_buffer);
 	if (size <= RPC_BUFFER_MAXSIZE)
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -665,8 +665,10 @@ xprt_rdma_allocate(struct rpc_task *task
 	gfp_t flags;
 
 	flags = RPCRDMA_DEF_GFP;
+	if (RPC_IS_ASYNC(task))
+		flags = GFP_NOWAIT | __GFP_NOWARN;
 	if (RPC_IS_SWAPPER(task))
-		flags = __GFP_MEMALLOC | GFP_NOWAIT | __GFP_NOWARN;
+		flags |= __GFP_MEMALLOC;
 
 	if (!rpcrdma_get_sendbuf(r_xprt, req, rqst->rq_callsize, flags))
 		goto out_fail;