netdev - [PATCH bpf 2/3] libbpf: restore umem state after socket create failure

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Date:   Wed, 24 Mar 2021 14:13:36 +0000
From:   Ciara Loftus <ciara.loftus@...el.com>
To:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        magnus.karlsson@...el.com, bjorn@...nel.org
Cc:     Ciara Loftus <ciara.loftus@...el.com>
Subject: [PATCH bpf 2/3] libbpf: restore umem state after socket create failure

If the call to socket_create fails, the user may want to retry the
socket creation using the same umem. Ensure that the umem is in the
same state on exit if the call failed by restoring the _save pointers
and not unmapping the set of umem rings if those pointers are non NULL.

Fixes: 2f6324a3937f ("libbpf: Support shared umems between queues and devices")

Signed-off-by: Ciara Loftus <ciara.loftus@...el.com>
---
 tools/lib/bpf/xsk.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 443b0cfb45e8..ec3c23299329 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -743,21 +743,23 @@ static struct xsk_ctx *xsk_get_ctx(struct xsk_umem *umem, int ifindex,
 	return NULL;
 }
 
-static void xsk_put_ctx(struct xsk_ctx *ctx)
+static void xsk_put_ctx(struct xsk_ctx *ctx, bool unmap)
 {
 	struct xsk_umem *umem = ctx->umem;
 	struct xdp_mmap_offsets off;
 	int err;
 
 	if (--ctx->refcount == 0) {
-		err = xsk_get_mmap_offsets(umem->fd, &off);
-		if (!err) {
-			munmap(ctx->fill->ring - off.fr.desc,
-			       off.fr.desc + umem->config.fill_size *
-			       sizeof(__u64));
-			munmap(ctx->comp->ring - off.cr.desc,
-			       off.cr.desc + umem->config.comp_size *
-			       sizeof(__u64));
+		if (unmap) {
+			err = xsk_get_mmap_offsets(umem->fd, &off);
+			if (!err) {
+				munmap(ctx->fill->ring - off.fr.desc,
+				       off.fr.desc + umem->config.fill_size *
+				sizeof(__u64));
+				munmap(ctx->comp->ring - off.cr.desc,
+				       off.cr.desc + umem->config.comp_size *
+				sizeof(__u64));
+			}
 		}
 
 		list_del(&ctx->list);
@@ -854,6 +856,9 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 	struct xsk_socket *xsk;
 	struct xsk_ctx *ctx;
 	int err, ifindex;
+	struct xsk_ring_prod *fsave = umem->fill_save;
+	struct xsk_ring_cons *csave = umem->comp_save;
+	bool unmap = !fsave;
 
 	if (!umem || !xsk_ptr || !(rx || tx))
 		return -EFAULT;
@@ -1005,7 +1010,9 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 		munmap(rx_map, off.rx.desc +
 		       xsk->config.rx_size * sizeof(struct xdp_desc));
 out_put_ctx:
-	xsk_put_ctx(ctx);
+	umem->fill_save = fsave;
+	umem->comp_save = csave;
+	xsk_put_ctx(ctx, unmap);
 out_socket:
 	if (--umem->refcount)
 		close(xsk->fd);
@@ -1071,7 +1078,7 @@ void xsk_socket__delete(struct xsk_socket *xsk)
 		}
 	}
 
-	xsk_put_ctx(ctx);
+	xsk_put_ctx(ctx, true);
 
 	umem->refcount--;
 	/* Do not close an fd that also has an associated umem connected
-- 
2.17.1