gro_cell: add napi_disable in gro_cells_destroy

[ Upstream commit 8e1da73acded4751a93d4166458a7e640f37d26c ]

Add napi_disable routine in gro_cells_destroy since starting from
commit c42858ea ("gro_cells: remove spinlock protecting receive
queues") gro_cell_poll and gro_cells_destroy can run concurrently on
napi_skbs list producing a kernel Oops if the tunnel interface is
removed while gro_cell_poll is running. The following Oops has been
triggered removing a vxlan device while the interface is receiving
traffic

[ 5628.948853] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
[ 5628.949981] PGD 0 P4D 0
[ 5628.950308] Oops: 0002 [#1] SMP PTI
[ 5628.950748] CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 4.20.0-rc6+ #41
[ 5628.952940] RIP: 0010:gro_cell_poll+0x49/0x80
[ 5628.955615] RSP: 0018:ffffc9000004fdd8 EFLAGS: 00010202
[ 5628.956250] RAX: 0000000000000000 RBX: ffffe8ffffc08150 RCX: 0000000000000000
[ 5628.957102] RDX: 0000000000000000 RSI: ffff88802356bf00 RDI: ffffe8ffffc08150
[ 5628.957940] RBP: 0000000000000026 R08: 0000000000000000 R09: 0000000000000000
[ 5628.958803] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000040
[ 5628.959661] R13: ffffe8ffffc08100 R14: 0000000000000000 R15: 0000000000000040
[ 5628.960682] FS:  0000000000000000(0000) GS:ffff88803ea00000(0000) knlGS:0000000000000000
[ 5628.961616] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 5628.962359] CR2: 0000000000000008 CR3: 000000000221c000 CR4: 00000000000006b0
[ 5628.963188] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 5628.964034] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 5628.964871] Call Trace:
[ 5628.965179]  net_rx_action+0xf0/0x380
[ 5628.965637]  __do_softirq+0xc7/0x431
[ 5628.966510]  run_ksoftirqd+0x24/0x30
[ 5628.966957]  smpboot_thread_fn+0xc5/0x160
[ 5628.967436]  kthread+0x113/0x130
[ 5628.968283]  ret_from_fork+0x3a/0x50
[ 5628.968721] Modules linked in:
[ 5628.969099] CR2: 0000000000000008
[ 5628.969510] ---[ end trace 9d9dedc7181661fe ]---
[ 5628.970073] RIP: 0010:gro_cell_poll+0x49/0x80
[ 5628.972965] RSP: 0018:ffffc9000004fdd8 EFLAGS: 00010202
[ 5628.973611] RAX: 0000000000000000 RBX: ffffe8ffffc08150 RCX: 0000000000000000
[ 5628.974504] RDX: 0000000000000000 RSI: ffff88802356bf00 RDI: ffffe8ffffc08150
[ 5628.975462] RBP: 0000000000000026 R08: 0000000000000000 R09: 0000000000000000
[ 5628.976413] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000040
[ 5628.977375] R13: ffffe8ffffc08100 R14: 0000000000000000 R15: 0000000000000040
[ 5628.978296] FS:  0000000000000000(0000) GS:ffff88803ea00000(0000) knlGS:0000000000000000
[ 5628.979327] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 5628.980044] CR2: 0000000000000008 CR3: 000000000221c000 CR4: 00000000000006b0
[ 5628.980929] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 5628.981736] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 5628.982409] Kernel panic - not syncing: Fatal exception in interrupt
[ 5628.983307] Kernel Offset: disabled

Fixes: c42858ea ("gro_cells: remove spinlock protecting receive queues")
Signed-off-by: NLorenzo Bianconi <lorenzo.bianconi@redhat.com>
Acked-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

net/core/gro_cells.c

@@ -84,6 +84,7 @@ void gro_cells_destroy(struct gro_cells *gcells)
 	for_each_possible_cpu(i) {
 		struct gro_cell *cell = per_cpu_ptr(gcells->cells, i);
 
+		napi_disable(&cell->napi);
 		netif_napi_del(&cell->napi);
 		__skb_queue_purge(&cell->napi_skbs);
 	}