linux-kernel - [PATCH 4.9 183/218] SUNRPC/call_alloc: async tasks mustnt block waiting for memory

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Message-Id: <20220418121206.237161544@linuxfoundation.org>
Date:   Mon, 18 Apr 2022 14:14:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, NeilBrown <neilb@...e.de>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 183/218] SUNRPC/call_alloc: async tasks mustnt block waiting for memory

From: NeilBrown <neilb@...e.de>

[ Upstream commit c487216bec83b0c5a8803e5c61433d33ad7b104d ]

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@...e.de>
Signed-off-by: Trond Myklebust <trond.myklebust@...merspace.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/sunrpc/sched.c              | 4 +++-
 net/sunrpc/xprtrdma/transport.c | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 00d95fefdc6f..ccb9fa5812d8 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -883,8 +883,10 @@ 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)
diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index 3ea3bb64b6d5..f308f286e9aa 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -577,8 +577,10 @@ xprt_rdma_allocate(struct rpc_task *task)
 		return -ENOMEM;
 
 	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_rdmabuf(r_xprt, req, flags))
 		goto out_fail;
-- 
2.35.1