bpf: Clear pfmemalloc flag when freeing all fragments

It is possible for bpf_xdp_adjust_tail() to free all fragments. The
kfunc currently clears the XDP_FLAGS_HAS_FRAGS bit, but not
XDP_FLAGS_FRAGS_PF_MEMALLOC. So far, this has not caused a issue when
building sk_buff from xdp_buff since all readers of xdp_buff->flags
use the flag only when there are fragments. Clear the
XDP_FLAGS_FRAGS_PF_MEMALLOC bit as well to make the flags correct.

Signed-off-by: Amery Hung <[email protected]>
Signed-off-by: Martin KaFai Lau <[email protected]>
Reviewed-by: Maciej Fijalkowski <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: ameryhung

include/net/xdp.h

@@ -115,6 +115,11 @@ static __always_inline void xdp_buff_set_frag_pfmemalloc(struct xdp_buff *xdp)
 	xdp->flags |= XDP_FLAGS_FRAGS_PF_MEMALLOC;
 }
 
+static __always_inline void xdp_buff_clear_frag_pfmemalloc(struct xdp_buff *xdp)
+{
+	xdp->flags &= ~XDP_FLAGS_FRAGS_PF_MEMALLOC;
+}
+
 static __always_inline void
 xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
 {

net/core/filter.c

@@ -4210,6 +4210,7 @@ static int bpf_xdp_frags_shrink_tail(struct xdp_buff *xdp, int offset)
 
 	if (unlikely(!sinfo->nr_frags)) {
 		xdp_buff_clear_frags_flag(xdp);
+		xdp_buff_clear_frag_pfmemalloc(xdp);
 		xdp->data_end -= offset;
 	}