net: allow skb_datagram_iter to be called from any context

JIRA: https://issues.redhat.com/browse/RHEL-46610
Tested: LNST

Upstream commit:
commit d2d30a3
Author: Sagi Grimberg <sagi@grimberg.me>
Date:   Wed Jun 26 13:00:08 2024 +0300

    net: allow skb_datagram_iter to be called from any context

    We only use the mapping in a single context, so kmap_local is sufficient
    and cheaper. Make sure to use skb_frag_foreach_page as skb frags may
    contain compound pages and we need to map page by page.

    Reported-by: kernel test robot <oliver.sang@intel.com>
    Closes: https://lore.kernel.org/oe-lkp/202406161539.b5ff7b20-oliver.sang@intel.com
    Fixes: 950fcae ("datagram: consolidate datagram copy to iter helpers")
    Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
    Link: https://patch.msgid.link/20240626100008.831849-1-sagi@grimberg.me
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: Paolo Abeni

net/core/datagram.c

@@ -434,15 +434,22 @@ static int __skb_datagram_iter(const struct sk_buff *skb, int offset,
 
 		end = start + skb_frag_size(frag);
 		if ((copy = end - offset) > 0) {
-			struct page *page = skb_frag_page(frag);
-			u8 *vaddr = kmap(page);
+			u32 p_off, p_len, copied;
+			struct page *p;
+			u8 *vaddr;
 
 			if (copy > len)
 				copy = len;
-			n = INDIRECT_CALL_1(cb, simple_copy_to_iter,
-					vaddr + skb_frag_off(frag) + offset - start,
-					copy, data, to);
-			kunmap(page);
+
+			skb_frag_foreach_page(frag,
+					      skb_frag_off(frag) + offset - start,
+					      copy, p, p_off, p_len, copied) {
+				vaddr = kmap_local_page(p);
+				n = INDIRECT_CALL_1(cb, simple_copy_to_iter,
+					vaddr + p_off, p_len, data, to);
+				kunmap_local(vaddr);
+			}
+
 			offset += n;
 			if (n != copy)
 				goto short_copy;