diff mbox series

[bpf-next,17/17] net: ti: remove rcu_read_lock() around XDP program invocation

Message ID 20210609103326.278782-18-toke@redhat.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Clean up and document RCU-based object protection for XDP_REDIRECT | expand

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Commit Message

Toke Høiland-Jørgensen June 9, 2021, 10:33 a.m. UTC
The cpsw driver has rcu_read_lock()/rcu_read_unlock() pairs around XDP
program invocations. However, the actual lifetime of the objects referred
by the XDP program invocation is longer, all the way through to the call to
xdp_do_flush(), making the scope of the rcu_read_lock() too small. This
turns out to be harmless because it all happens in a single NAPI poll
cycle (and thus under local_bh_disable()), but it makes the rcu_read_lock()
misleading.

Rather than extend the scope of the rcu_read_lock(), just get rid of it
entirely. With the addition of RCU annotations to the XDP_REDIRECT map
types that take bh execution into account, lockdep even understands this to
be safe, so there's really no reason to keep it around.

Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 drivers/net/ethernet/ti/cpsw_priv.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

Comments

Grygorii Strashko June 9, 2021, 5:04 p.m. UTC | #1
On 09/06/2021 13:33, Toke Høiland-Jørgensen wrote:
> The cpsw driver has rcu_read_lock()/rcu_read_unlock() pairs around XDP
> program invocations. However, the actual lifetime of the objects referred
> by the XDP program invocation is longer, all the way through to the call to
> xdp_do_flush(), making the scope of the rcu_read_lock() too small. This
> turns out to be harmless because it all happens in a single NAPI poll
> cycle (and thus under local_bh_disable()), but it makes the rcu_read_lock()
> misleading.
> 
> Rather than extend the scope of the rcu_read_lock(), just get rid of it
> entirely. With the addition of RCU annotations to the XDP_REDIRECT map
> types that take bh execution into account, lockdep even understands this to
> be safe, so there's really no reason to keep it around.
> 
> Cc: Grygorii Strashko <grygorii.strashko@ti.com>
> Cc: linux-omap@vger.kernel.org
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---
>   drivers/net/ethernet/ti/cpsw_priv.c | 10 ++--------
>   1 file changed, 2 insertions(+), 8 deletions(-)

Tested-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
diff mbox series

Patch

diff --git a/drivers/net/ethernet/ti/cpsw_priv.c b/drivers/net/ethernet/ti/cpsw_priv.c
index 5862f0a4a975..ecc2a6b7e28f 100644
--- a/drivers/net/ethernet/ti/cpsw_priv.c
+++ b/drivers/net/ethernet/ti/cpsw_priv.c
@@ -1328,13 +1328,9 @@  int cpsw_run_xdp(struct cpsw_priv *priv, int ch, struct xdp_buff *xdp,
 	struct bpf_prog *prog;
 	u32 act;
 
-	rcu_read_lock();
-
 	prog = READ_ONCE(priv->xdp_prog);
-	if (!prog) {
-		ret = CPSW_XDP_PASS;
-		goto out;
-	}
+	if (!prog)
+		return CPSW_XDP_PASS;
 
 	act = bpf_prog_run_xdp(prog, xdp);
 	/* XDP prog might have changed packet data and boundaries */
@@ -1378,10 +1374,8 @@  int cpsw_run_xdp(struct cpsw_priv *priv, int ch, struct xdp_buff *xdp,
 	ndev->stats.rx_bytes += *len;
 	ndev->stats.rx_packets++;
 out:
-	rcu_read_unlock();
 	return ret;
 drop:
-	rcu_read_unlock();
 	page_pool_recycle_direct(cpsw->page_pool[ch], page);
 	return ret;
 }