[PATCH net v2] nfp: fix rcu_read_lock/unlock while rcu_derefrencing

[Louis Peens <louis.peens@xxxxxxxxxxxx>]

From: Tianyu Yuan <tianyu.yuan@xxxxxxxxxxxx>

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")
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Tianyu Yuan <tianyu.yuan@xxxxxxxxxxxx>
Acked-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
Signed-off-by: Louis Peens <louis.peens@xxxxxxxxxxxx>
---
v1 -> v2:
   Remove unnessary nfp_app_dev_get_locked() helper function
   Replace rcu_dereference() with rcu_dereference_check() in .get_dev()
   Improve commit message
---
 drivers/net/ethernet/netronome/nfp/abm/main.c    | 4 ++--
 drivers/net/ethernet/netronome/nfp/flower/main.c | 5 +++--
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/netronome/nfp/abm/main.c b/drivers/net/ethernet/netronome/nfp/abm/main.c
index 5d3df28c648f..10b73297a313 100644
--- a/drivers/net/ethernet/netronome/nfp/abm/main.c
+++ b/drivers/net/ethernet/netronome/nfp/abm/main.c
@@ -63,14 +63,14 @@ nfp_abm_repr_get(struct nfp_app *app, u32 port_id, bool *redir_egress)
 	rtype = FIELD_GET(NFP_ABM_PORTID_TYPE, port_id);
 	port = FIELD_GET(NFP_ABM_PORTID_ID, port_id);
 
-	reprs = rcu_dereference(app->reprs[rtype]);
+	reprs = rcu_dereference_check(app->reprs[rtype], rcu_read_lock_bh_held());
 	if (!reprs)
 		return NULL;
 
 	if (port >= reprs->num_reprs)
 		return NULL;
 
-	return rcu_dereference(reprs->reprs[port]);
+	return rcu_dereference_check(reprs->reprs[port], rcu_read_lock_bh_held());
 }
 
 static int
diff --git a/drivers/net/ethernet/netronome/nfp/flower/main.c b/drivers/net/ethernet/netronome/nfp/flower/main.c
index 83eaa5ae3cd4..d33cc22c788d 100644
--- a/drivers/net/ethernet/netronome/nfp/flower/main.c
+++ b/drivers/net/ethernet/netronome/nfp/flower/main.c
@@ -257,14 +257,15 @@ nfp_flower_dev_get(struct nfp_app *app, u32 port_id, bool *redir_egress)
 	if (repr_type > NFP_REPR_TYPE_MAX)
 		return NULL;
 
-	reprs = rcu_dereference(app->reprs[repr_type]);
+	reprs = rcu_dereference_check(app->reprs[repr_type],
+				      rcu_read_lock_bh_held());
 	if (!reprs)
 		return NULL;
 
 	if (port >= reprs->num_reprs)
 		return NULL;
 
-	return rcu_dereference(reprs->reprs[port]);
+	return rcu_dereference_check(reprs->reprs[port], rcu_read_lock_bh_held());
 }
 
 static int
-- 
2.34.1