xfrm: Fix RCU vs hash_resize_mutex lock inversion

xfrm_bydst_resize() calls synchronize_rcu() while holding
hash_resize_mutex. But then on PREEMPT_RT configurations,
xfrm_policy_lookup_bytype() may acquire that mutex while running in an
RCU read side critical section. This results in a deadlock.

In fact the scope of hash_resize_mutex is way beyond the purpose of
xfrm_policy_lookup_bytype() to just fetch a coherent and stable policy
for a given destination/direction, along with other details.

The lower level net->xfrm.xfrm_policy_lock, which among other things
protects per destination/direction references to policy entries, is
enough to serialize and benefit from priority inheritance against the
write side. As a bonus, it makes it officially a per network namespace
synchronization business where a policy table resize on namespace A
shouldn't block a policy lookup on namespace B.

Fixes: 77cc278f7b20 (xfrm: policy: Use sequence counters with associated lock)
Cc: [email protected]
Cc: Ahmed S. Darwish <[email protected]>
Cc: Peter Zijlstra (Intel) <[email protected]>
Cc: Varad Gautam <[email protected]>
Cc: Steffen Klassert <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: David S. Miller <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Steffen Klassert <[email protected]>

0 files changed, 0 insertions, 0 deletions