Commit a7210354 authored by NeilBrown's avatar NeilBrown Committed by Trond Myklebust
Browse files

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



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.

xprt_dynamic_alloc_slot can block indefinitely.  This can tie up all
workqueue threads and NFS can deadlock.  So when called from a
workqueue, set __GFP_NORETRY.

The rdma alloc_slot already does not block.  However it sets the error
to -EAGAIN suggesting this will trigger a sleep.  It does not.  As we
can see in call_reserveresult(), only -ENOMEM causes a sleep.  -EAGAIN
causes immediate retry.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@hammerspace.com>
parent a41b05ed

net/sunrpc/xprt.c

+4 −1
Original line number Diff line number Diff line
@@ -1687,12 +1687,15 @@ static bool xprt_throttle_congested(struct rpc_xprt *xprt, struct rpc_task *task 
static struct rpc_rqst *xprt_dynamic_alloc_slot(struct rpc_xprt *xprt)

{

	struct rpc_rqst *req = ERR_PTR(-EAGAIN);

	gfp_t gfp_mask = GFP_KERNEL;



	if (xprt->num_reqs >= xprt->max_reqs)

		goto out;

	++xprt->num_reqs;

	spin_unlock(&xprt->reserve_lock);

	req = kzalloc(sizeof(struct rpc_rqst), GFP_KERNEL);

	if (current->flags & PF_WQ_WORKER)

		gfp_mask |= __GFP_NORETRY | __GFP_NOWARN;

	req = kzalloc(sizeof(*req), gfp_mask);

	spin_lock(&xprt->reserve_lock);

	if (req != NULL)

		goto out;

net/sunrpc/xprtrdma/transport.c

+1 −1
Original line number Diff line number Diff line
@@ -517,7 +517,7 @@ xprt_rdma_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task) 
	return;



out_sleep:

	task->tk_status = -EAGAIN;

	task->tk_status = -ENOMEM;

	xprt_add_backlog(xprt, task);

}