SUNRPC/call_alloc: async tasks mustn't block waiting for memory

BugLink: https://bugs.launchpad.net/bugs/1971497
[ 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@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 8fc4a6b3422f46a2e16d0c51ec16556b9892084d..32ffa801a5b9788005eacbe184b3c1258f7511e8 100644 (file)
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -1039,8 +1039,10 @@ int rpc_malloc(struct rpc_task *task)
        struct rpc_buffer *buf;
        gfp_t gfp = GFP_NOFS;
 
+       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 2f21e3c52bfc13067166de440157d8ba5ab88bdf..866bcd99bdc0e07fa8d1d5daacdb0b644739b0a6 100644 (file)
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -626,8 +626,10 @@ 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_check_regbuf(r_xprt, req->rl_sendbuf, rqst->rq_callsize,
                                  flags))