Re: [PATCH net 1/1] xdp: fix xdp_return_frame() kernel BUG throw for page_pool memory model
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From: Jesper Dangaard Brouer <hidden>
Date: 2021-03-29 15:03:12
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On Mon, 29 Mar 2021 16:00:39 +0800 Ong Boon Leong [off-list ref] wrote:
xdp_return_frame() may be called outside of NAPI context to return
xdpf back to page_pool. xdp_return_frame() calls __xdp_return() with
napi_direct = false. For page_pool memory model, __xdp_return() calls
xdp_return_frame_no_direct() unconditionally and below false negative
kernel BUG throw happened under preempt-rt build:
[ 430.450355] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/3884
[ 430.451678] caller is __xdp_return+0x1ff/0x2e0
[ 430.452111] CPU: 0 PID: 3884 Comm: modprobe Tainted: G U E 5.12.0-rc2+ #45
So, this patch fixes the issue by adding "if (napi_direct)" condition
to skip calling xdp_return_frame_no_direct() if napi_direct = false.
Fixes: 2539650fadbf ("xdp: Helpers for disabling napi_direct of xdp_return_frame")
Signed-off-by: Ong Boon Leong <redacted>
---This looks correct to me. Acked-by: Jesper Dangaard Brouer <redacted>
quoted hunk ↗ jump to hunk
net/core/xdp.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/net/core/xdp.c b/net/core/xdp.c index 05354976c1fc..4eaa28972af2 100644 --- a/net/core/xdp.c +++ b/net/core/xdp.c@@ -350,7 +350,8 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct, /* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */ xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params); page = virt_to_head_page(data); - napi_direct &= !xdp_return_frame_no_direct(); + if (napi_direct) + napi_direct &= !xdp_return_frame_no_direct();
if (napi_direct && xdp_return_frame_no_direct()) napi_direct = false; I wonder if this code would be easier to understand?
page_pool_put_full_page(xa->page_pool, page, napi_direct); rcu_read_unlock(); break;
-- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer