From: Frederic Weisbecker <frederic@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx
Cc: Ahmed S. Darwish <a.darwish@xxxxxxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Varad Gautam <varad.gautam@xxxxxxxx>
Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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_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))
@@ -4123,6 +4122,7 @@ 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);
@@ -4167,7 +4167,6 @@ 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
