net: msg_zerocopy: elide page accounting if RLIM_INFINITY

MSG_ZEROCOPY ensures that pinned user pages do not exceed the limit.
If no limit is set, skip this accounting as otherwise expensive
atomic_long operations are called for no reason.

This accounting is already skipped for privileged (CAP_IPC_LOCK)
users. Rely on the same mechanism: if no mmp->user is set,
mm_unaccount_pinned_pages does not decrement either.

Tested by running tools/testing/selftests/net/msg_zerocopy.sh with
an unprivileged user for the TXMODE binary:

    ip netns exec "${NS1}" sudo -u "{$USER}" "${BIN}" "-${IP}" ...

Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230214155740.3448763-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 13ea10c..98ebce9 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1406,14 +1406,18 @@ EXPORT_SYMBOL_GPL(skb_morph);
 
 int mm_account_pinned_pages(struct mmpin *mmp, size_t size)
 {
-       unsigned long max_pg, num_pg, new_pg, old_pg;
+       unsigned long max_pg, num_pg, new_pg, old_pg, rlim;
        struct user_struct *user;
 
        if (capable(CAP_IPC_LOCK) || !size)
                return 0;
 
+       rlim = rlimit(RLIMIT_MEMLOCK);
+       if (rlim == RLIM_INFINITY)
+               return 0;
+
        num_pg = (size >> PAGE_SHIFT) + 2;      /* worst case */
-       max_pg = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+       max_pg = rlim >> PAGE_SHIFT;
        user = mmp->user ? : current_user();
 
        old_pg = atomic_long_read(&user->locked_vm);