Re: [PATCH 3/3] netlink: Lock out table resizes while dumping Netlink sockets
From: Patrick McHardy <hidden>
Date: 2015-01-20 14:31:54
Also in:
netfilter-devel
On 20.01, Thomas Graf wrote:
Lock out table resizes while dumping Netlink sockets to user space. This keeps disruptions to a minimum for readers which don't handle the NLM_F_DUMP_INTR flag.
This doesn't lock them out for the duration of the entire dump of course, so the benefit seems rather small. Still with this patch, they will need to handle NLM_F_DUMP_INTR or will get unpredictable behaviour, in which case I'd think it makes more sense to not even try this, all it does is hide parts of the brokenness. An alternative would be to set a flag in ht when a dump begins that indicates to skip resizing operations and on the end of the dump perform any resizing operations that might be necessary. Herbert disagrees though and he might be right.
quoted hunk ↗ jump to hunk
Signed-off-by: Thomas Graf <tgraf@suug.ch> --- net/netlink/diag.c | 3 +++ 1 file changed, 3 insertions(+)diff --git a/net/netlink/diag.c b/net/netlink/diag.c index 50aa385..be4ea6e 100644 --- a/net/netlink/diag.c +++ b/net/netlink/diag.c@@ -114,6 +114,8 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb, req = nlmsg_data(cb->nlh); cb->seq = atomic_read(&nl_table_seq); + mutex_lock(&ht->mutex); + for (i = 0; i < htbl->size; i++) { struct rhash_head *pos;@@ -161,6 +163,7 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb, num++; } done: + mutex_unlock(&ht->mutex); cb->args[0] = num; cb->args[1] = protocol;-- 1.9.3