| 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| State | Superseded |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 |
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 --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; }
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(-)