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[45/47] netfilter: x_tables: Add note about how to free percpu counters

Message ID 20180330114619.18797-6-pablo@netfilter.org
State Accepted, archived
Delegated to: David Miller
Headers show
Series [01/47] netfilter: nf_tables: nf_tables_obj_lookup_byhandle() can be static | expand

Commit Message

Pablo Neira Ayuso March 30, 2018, 11:46 a.m. UTC 
From: Ben Hutchings <ben.hutchings@codethink.co.uk>

Due to the way percpu counters are allocated and freed in blocks,
it is not safe to free counters individually.  Currently all callers
do the right thing, but let's note this restriction.

Fixes: ae0ac0ed6fcf ("netfilter: x_tables: pack percpu counter allocations")
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/x_tables.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index bac932f1c582..75cd5196b29b 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -1854,7 +1854,9 @@  EXPORT_SYMBOL_GPL(xt_proto_fini);
  * to fetch the real percpu counter.
  *
  * To speed up allocation and improve data locality, a 4kb block is
- * allocated.
+ * allocated.  Freeing any counter may free an entire block, so all
+ * counters allocated using the same state must be freed at the same
+ * time.
  *
  * xt_percpu_counter_alloc_state contains the base address of the
  * allocated page and the current sub-offset.