On Thu, 15 Jun 2023 09:31:39 +0200 Louis Peens wrote:
From: Tianyu Yuan tianyu.yuan@corigine.com
When CONFIG_PROVE_LOCKING and CONFIG_PROVE_RCU are enabled, using OVS with vf reprs on bridge will lead to following log in dmesg:
.../nfp/flower/main.c:269 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1 no locks held by swapper/15/0.
...... Call Trace:
<IRQ> dump_stack_lvl+0x8c/0xa0 lockdep_rcu_suspicious+0x118/0x1a0 nfp_flower_dev_get+0xc1/0x240 [nfp] nfp_nfd3_rx+0x419/0xb90 [nfp] ? validate_chain+0x640/0x1880 nfp_nfd3_poll+0x3e/0x180 [nfp] __napi_poll+0x28/0x1d0 net_rx_action+0x2bd/0x3c0 ? _raw_spin_unlock_irqrestore+0x42/0x70 __do_softirq+0xc3/0x3c6 irq_exit_rcu+0xeb/0x130 common_interrupt+0xb9/0xd0 </IRQ> <TASK> ...... </TASK>
In previous patch rcu_read_lock()/unlock() are removed because rcu-lock may affect xdp_prog. However this removal will make RCU lockdep report above warning because of missing of rcu_read_lock()/unlock() pair around rcu_deference().
This patch resolves this problem by replacing rcu_deference() with rcu_dereference_check() to annotate that access is safe if rcu_read_lock/rcu_read_lock_bh is held.
Fixes: d5789621b658 ("nfp: Remove rcu_read_lock() around XDP program invocation")
I'd vote to simply revert that commit. Toke likely assumed that the RCU protection is only for XDP but turns out we have more datapath stuff that depends on it. No strong preference but my vote would be to not play with RCU flavors at the driver level.
CC: stable@vger.kernel.org Signed-off-by: Tianyu Yuan tianyu.yuan@corigine.com Acked-by: Simon Horman simon.horman@corigine.com Signed-off-by: Louis Peens louis.peens@corigine.com
- reprs = rcu_dereference(app->reprs[rtype]);
- reprs = rcu_dereference_check(app->reprs[rtype], rcu_read_lock_bh_held());
If you prefer to keep the patch I think this is just rcu_dereference_bh() ?