RDMA/siw: Add sendpage_ok() check to disable MSG_SPLICE_PAGES

While running ISER over SIW, the initiator machine encounters a warning
from skb_splice_from_iter() indicating that a slab page is being used in
send_page. To address this, it is better to add a sendpage_ok() check
within the driver itself, and if it returns 0, then MSG_SPLICE_PAGES flag
should be disabled before entering the network stack.

A similar issue has been discussed for NVMe in this thread:
https://lore.kernel.org/all/[email protected]/

  WARNING: CPU: 0 PID: 5342 at net/core/skbuff.c:7140 skb_splice_from_iter+0x173/0x320
  Call Trace:
   tcp_sendmsg_locked+0x368/0xe40
   siw_tx_hdt+0x695/0xa40 [siw]
   siw_qp_sq_process+0x102/0xb00 [siw]
   siw_sq_resume+0x39/0x110 [siw]
   siw_run_sq+0x74/0x160 [siw]
   kthread+0xd2/0x100
   ret_from_fork+0x34/0x40
   ret_from_fork_asm+0x1a/0x30

Link: https://patch.msgid.link/r/[email protected]
Signed-off-by: Showrya M N <[email protected]>
Signed-off-by: Potnuri Bharat Teja <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: Showrya M N

drivers/infiniband/sw/siw/siw_qp_tx.c

@@ -331,6 +331,8 @@ static int siw_tcp_sendpages(struct socket *s, struct page **page, int offset,
 			msg.msg_flags &= ~MSG_MORE;
 
 		tcp_rate_check_app_limited(sk);
+		if (!sendpage_ok(page[i]))
+			msg.msg_flags &= ~MSG_SPLICE_PAGES;
 		bvec_set_page(&bvec, page[i], bytes, offset);
 		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);