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Subject[PATCH 4.18 066/197] net/xdp: Fix suspicious RCU usage warning
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tariq Toukan <tariqt@mellanox.com>

[ Upstream commit 21b172ee11b6ec260bd7e6a27b11a8a8d392fce5 ]

Fix the warning below by calling rhashtable_lookup_fast.
Also, make some code movements for better quality and human
readability.

[ 342.450870] WARNING: suspicious RCU usage
[ 342.455856] 4.18.0-rc2+ #17 Tainted: G O
[ 342.462210] -----------------------------
[ 342.467202] ./include/linux/rhashtable.h:481 suspicious rcu_dereference_check() usage!
[ 342.476568]
[ 342.476568] other info that might help us debug this:
[ 342.476568]
[ 342.486978]
[ 342.486978] rcu_scheduler_active = 2, debug_locks = 1
[ 342.495211] 4 locks held by modprobe/3934:
[ 342.500265] #0: 00000000e23116b2 (mlx5_intf_mutex){+.+.}, at:
mlx5_unregister_interface+0x18/0x90 [mlx5_core]
[ 342.511953] #1: 00000000ca16db96 (rtnl_mutex){+.+.}, at: unregister_netdev+0xe/0x20
[ 342.521109] #2: 00000000a46e2c4b (&priv->state_lock){+.+.}, at: mlx5e_close+0x29/0x60
[mlx5_core]
[ 342.531642] #3: 0000000060c5bde3 (mem_id_lock){+.+.}, at: xdp_rxq_info_unreg+0x93/0x6b0
[ 342.541206]
[ 342.541206] stack backtrace:
[ 342.547075] CPU: 12 PID: 3934 Comm: modprobe Tainted: G O 4.18.0-rc2+ #17
[ 342.556621] Hardware name: Dell Inc. PowerEdge R730/0H21J3, BIOS 1.5.4 10/002/2015
[ 342.565606] Call Trace:
[ 342.568861] dump_stack+0x78/0xb3
[ 342.573086] xdp_rxq_info_unreg+0x3f5/0x6b0
[ 342.578285] ? __call_rcu+0x220/0x300
[ 342.582911] mlx5e_free_rq+0x38/0xc0 [mlx5_core]
[ 342.588602] mlx5e_close_channel+0x20/0x120 [mlx5_core]
[ 342.594976] mlx5e_close_channels+0x26/0x40 [mlx5_core]
[ 342.601345] mlx5e_close_locked+0x44/0x50 [mlx5_core]
[ 342.607519] mlx5e_close+0x42/0x60 [mlx5_core]
[ 342.613005] __dev_close_many+0xb1/0x120
[ 342.617911] dev_close_many+0xa2/0x170
[ 342.622622] rollback_registered_many+0x148/0x460
[ 342.628401] ? __lock_acquire+0x48d/0x11b0
[ 342.633498] ? unregister_netdev+0xe/0x20
[ 342.638495] rollback_registered+0x56/0x90
[ 342.643588] unregister_netdevice_queue+0x7e/0x100
[ 342.649461] unregister_netdev+0x18/0x20
[ 342.654362] mlx5e_remove+0x2a/0x50 [mlx5_core]
[ 342.659944] mlx5_remove_device+0xe5/0x110 [mlx5_core]
[ 342.666208] mlx5_unregister_interface+0x39/0x90 [mlx5_core]
[ 342.673038] cleanup+0x5/0xbfc [mlx5_core]
[ 342.678094] __x64_sys_delete_module+0x16b/0x240
[ 342.683725] ? do_syscall_64+0x1c/0x210
[ 342.688476] do_syscall_64+0x5a/0x210
[ 342.693025] entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fixes: 8d5d88527587 ("xdp: rhashtable with allocator ID to pointer mapping")
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/xdp.c | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)

--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -95,23 +95,15 @@ static void __xdp_rxq_info_unreg_mem_mod
{
struct xdp_mem_allocator *xa;
int id = xdp_rxq->mem.id;
- int err;

if (id == 0)
return;

mutex_lock(&mem_id_lock);

- xa = rhashtable_lookup(mem_id_ht, &id, mem_id_rht_params);
- if (!xa) {
- mutex_unlock(&mem_id_lock);
- return;
- }
-
- err = rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params);
- WARN_ON(err);
-
- call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
+ xa = rhashtable_lookup_fast(mem_id_ht, &id, mem_id_rht_params);
+ if (xa && !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);
}

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