On Thu, Jun 17, 2021 at 11:27:47PM +0200, Toke Høiland-Jørgensen wrote:

The stmmac 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: Giuseppe Cavallaro <redacted>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Jose Abreu <redacted>
Signed-off-by: Toke Høiland-Jørgensen <redacted>

Acked-by: Wong Vee Khee <redacted>
Tested-by: Song, Yoong Siang <redacted>

---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)