Patch "SUNRPC/xprt: async tasks mustn't block waiting for memory" has been added to the 5.16-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 5.16-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sunrpc-xprt-async-tasks-mustn-t-block-waiting-for-me.patch
and it can be found in the queue-5.16 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 52663508f4b611eff5b1da10eced77a96f7e7b77
Author: NeilBrown <neilb@xxxxxxx>
Date:   Mon Mar 7 10:41:44 2022 +1100

    SUNRPC/xprt: async tasks mustn't block waiting for memory
    
    [ Upstream commit a721035477fb5fb8abc738fbe410b07c12af3dc5 ]
    
    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: NeilBrown <neilb@xxxxxxx>
    Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 396a74974f60..75acde97d748 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1690,12 +1690,15 @@ 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_NOFS);
+	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;
diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index 6268af7e0310..256b06a92391 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -525,7 +525,7 @@ 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);
 }