From: Frederic Weisbecker frederic@kernel.org
commit 2580d3f40022642452dd8422bfb8c22e54cf84bb upstream.
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: stable@vger.kernel.org Cc: Ahmed S. Darwish a.darwish@linutronix.de Cc: Peter Zijlstra (Intel) peterz@infradead.org Cc: Varad Gautam varad.gautam@suse.com Cc: Steffen Klassert steffen.klassert@secunet.com Cc: Herbert Xu herbert@gondor.apana.org.au Cc: David S. Miller davem@davemloft.net Signed-off-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Steffen Klassert steffen.klassert@secunet.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/net/netns/xfrm.h | 1 + net/xfrm/xfrm_policy.c | 17 ++++++++--------- 2 files changed, 9 insertions(+), 9 deletions(-)
--- a/include/net/netns/xfrm.h +++ b/include/net/netns/xfrm.h @@ -74,6 +74,7 @@ struct netns_xfrm { #endif spinlock_t xfrm_state_lock; seqcount_spinlock_t xfrm_state_hash_generation; + seqcount_spinlock_t xfrm_policy_hash_generation;
spinlock_t xfrm_policy_lock; struct mutex xfrm_cfg_mutex; --- a/net/xfrm/xfrm_policy.c +++ b/net/xfrm/xfrm_policy.c @@ -155,7 +155,6 @@ static struct xfrm_policy_afinfo const _ __read_mostly;
static struct kmem_cache *xfrm_dst_cache __ro_after_init; -static __read_mostly seqcount_mutex_t xfrm_policy_hash_generation;
static struct rhashtable xfrm_policy_inexact_table; static const struct rhashtable_params xfrm_pol_inexact_params; @@ -585,7 +584,7 @@ static void xfrm_bydst_resize(struct net return;
spin_lock_bh(&net->xfrm.xfrm_policy_lock); - write_seqcount_begin(&xfrm_policy_hash_generation); + write_seqcount_begin(&net->xfrm.xfrm_policy_hash_generation);
odst = rcu_dereference_protected(net->xfrm.policy_bydst[dir].table, lockdep_is_held(&net->xfrm.xfrm_policy_lock)); @@ -596,7 +595,7 @@ static void xfrm_bydst_resize(struct net rcu_assign_pointer(net->xfrm.policy_bydst[dir].table, ndst); net->xfrm.policy_bydst[dir].hmask = nhashmask;
- write_seqcount_end(&xfrm_policy_hash_generation); + write_seqcount_end(&net->xfrm.xfrm_policy_hash_generation); spin_unlock_bh(&net->xfrm.xfrm_policy_lock);
synchronize_rcu(); @@ -1245,7 +1244,7 @@ static void xfrm_hash_rebuild(struct wor } while (read_seqretry(&net->xfrm.policy_hthresh.lock, seq));
spin_lock_bh(&net->xfrm.xfrm_policy_lock); - write_seqcount_begin(&xfrm_policy_hash_generation); + write_seqcount_begin(&net->xfrm.xfrm_policy_hash_generation);
/* make sure that we can insert the indirect policies again before * we start with destructive action. @@ -1354,7 +1353,7 @@ static void xfrm_hash_rebuild(struct wor
out_unlock: __xfrm_policy_inexact_flush(net); - write_seqcount_end(&xfrm_policy_hash_generation); + write_seqcount_end(&net->xfrm.xfrm_policy_hash_generation); spin_unlock_bh(&net->xfrm.xfrm_policy_lock);
mutex_unlock(&hash_resize_mutex); @@ -2095,9 +2094,9 @@ static struct xfrm_policy *xfrm_policy_l rcu_read_lock(); retry: do { - sequence = read_seqcount_begin(&xfrm_policy_hash_generation); + sequence = read_seqcount_begin(&net->xfrm.xfrm_policy_hash_generation); chain = policy_hash_direct(net, daddr, saddr, family, dir); - } while (read_seqcount_retry(&xfrm_policy_hash_generation, sequence)); + } while (read_seqcount_retry(&net->xfrm.xfrm_policy_hash_generation, sequence));
ret = NULL; hlist_for_each_entry_rcu(pol, chain, bydst) { @@ -2128,7 +2127,7 @@ static struct xfrm_policy *xfrm_policy_l }
skip_inexact: - if (read_seqcount_retry(&xfrm_policy_hash_generation, sequence)) + if (read_seqcount_retry(&net->xfrm.xfrm_policy_hash_generation, sequence)) goto retry;
if (ret && !xfrm_pol_hold_rcu(ret)) @@ -4084,6 +4083,7 @@ static int __net_init xfrm_net_init(stru /* Initialize the per-net locks here */ spin_lock_init(&net->xfrm.xfrm_state_lock); spin_lock_init(&net->xfrm.xfrm_policy_lock); + seqcount_spinlock_init(&net->xfrm.xfrm_policy_hash_generation, &net->xfrm.xfrm_policy_lock); mutex_init(&net->xfrm.xfrm_cfg_mutex);
rv = xfrm_statistics_init(net); @@ -4128,7 +4128,6 @@ void __init xfrm_init(void) { register_pernet_subsys(&xfrm_net_ops); xfrm_dev_init(); - seqcount_mutex_init(&xfrm_policy_hash_generation, &hash_resize_mutex); xfrm_input_init();
#ifdef CONFIG_XFRM_ESPINTCP