linux-kernel - [PATCH 5.4 34/37] xdp: obtain the mem_id mutex before trying to remove an entry.

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Date:   Tue, 17 Dec 2019 21:09:55 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Grygorii Strashko <grygorii.strashko@...com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 5.4 34/37] xdp: obtain the mem_id mutex before trying to remove an entry.

From: Jonathan Lemon <jonathan.lemon@...il.com>

[ Upstream commit 86c76c09898332143be365c702cf8d586ed4ed21 ]

A lockdep splat was observed when trying to remove an xdp memory
model from the table since the mutex was obtained when trying to
remove the entry, but not before the table walk started:

Fix the splat by obtaining the lock before starting the table walk.

Fixes: c3f812cea0d7 ("page_pool: do not release pool until inflight == 0.")
Reported-by: Grygorii Strashko <grygorii.strashko@...com>
Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
Tested-by: Grygorii Strashko <grygorii.strashko@...com>
Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/xdp.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -85,12 +85,8 @@ static void mem_xa_remove(struct xdp_mem
 {
 	trace_mem_disconnect(xa);
 
-	mutex_lock(&mem_id_lock);
-
 	if (!rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params))
 		call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
-
-	mutex_unlock(&mem_id_lock);
 }
 
 static void mem_allocator_disconnect(void *allocator)
@@ -98,6 +94,8 @@ static void mem_allocator_disconnect(voi
 	struct xdp_mem_allocator *xa;
 	struct rhashtable_iter iter;
 
+	mutex_lock(&mem_id_lock);
+
 	rhashtable_walk_enter(mem_id_ht, &iter);
 	do {
 		rhashtable_walk_start(&iter);
@@ -111,6 +109,8 @@ static void mem_allocator_disconnect(voi
 
 	} while (xa == ERR_PTR(-EAGAIN));
 	rhashtable_walk_exit(&iter);
+
+	mutex_unlock(&mem_id_lock);
 }
 
 static void mem_id_disconnect(int id)