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Commit 9c954201 authored by Daniel Borkmann's avatar Daniel Borkmann
Browse files

Merge branch 'bpf-fix-cpu-and-devmap-teardown' 



Jesper Dangaard Brouer says:

====================
Removing entries from cpumap and devmap, goes through a number of
syncronization steps to make sure no new xdp_frames can be enqueued.
But there is a small chance, that xdp_frames remains which have not
been flushed/processed yet.  Flushing these during teardown, happens
from RCU context and not as usual under RX NAPI context.

The optimization introduced in commt 389ab7f0 ("xdp: introduce
xdp_return_frame_rx_napi"), missed that the flush operation can also
be called from RCU context.  Thus, we cannot always use the
xdp_return_frame_rx_napi call, which take advantage of the protection
provided by XDP RX running under NAPI protection.

The samples/bpf xdp_redirect_cpu have a --stress-mode, that is
adjusted to easier reproduce (verified by Red Hat QA).
====================

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parents bf9bae0e 1bf9116d

kernel/bpf/cpumap.c

+9 −6
Original line number Diff line number Diff line
@@ -69,7 +69,7 @@ struct bpf_cpu_map { 
};



static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu,

			     struct xdp_bulk_queue *bq);

			     struct xdp_bulk_queue *bq, bool in_napi_ctx);



static u64 cpu_map_bitmap_size(const union bpf_attr *attr)

{
@@ -375,7 +375,7 @@ static void __cpu_map_entry_free(struct rcu_head *rcu) 
		struct xdp_bulk_queue *bq = per_cpu_ptr(rcpu->bulkq, cpu);



		/* No concurrent bq_enqueue can run at this point */

		bq_flush_to_queue(rcpu, bq);

		bq_flush_to_queue(rcpu, bq, false);

	}

	free_percpu(rcpu->bulkq);

	/* Cannot kthread_stop() here, last put free rcpu resources */
@@ -558,7 +558,7 @@ const struct bpf_map_ops cpu_map_ops = { 
};



static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu,

			     struct xdp_bulk_queue *bq)

			     struct xdp_bulk_queue *bq, bool in_napi_ctx)

{

	unsigned int processed = 0, drops = 0;

	const int to_cpu = rcpu->cpu;
@@ -578,7 +578,10 @@ static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu, 
		err = __ptr_ring_produce(q, xdpf);

		if (err) {

			drops++;

			if (likely(in_napi_ctx))

				xdp_return_frame_rx_napi(xdpf);

			else

				xdp_return_frame(xdpf);

		}

		processed++;

	}
@@ -598,7 +601,7 @@ static int bq_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_frame *xdpf) 
	struct xdp_bulk_queue *bq = this_cpu_ptr(rcpu->bulkq);



	if (unlikely(bq->count == CPU_MAP_BULK_SIZE))

		bq_flush_to_queue(rcpu, bq);

		bq_flush_to_queue(rcpu, bq, true);



	/* Notice, xdp_buff/page MUST be queued here, long enough for

	 * driver to code invoking us to finished, due to driver
@@ -661,7 +664,7 @@ void __cpu_map_flush(struct bpf_map *map) 


		/* Flush all frames in bulkq to real queue */

		bq = this_cpu_ptr(rcpu->bulkq);

		bq_flush_to_queue(rcpu, bq);

		bq_flush_to_queue(rcpu, bq, true);



		/* If already running, costs spin_lock_irqsave + smb_mb */

		wake_up_process(rcpu->kthread);

kernel/bpf/devmap.c

+9 −5
Original line number Diff line number Diff line
@@ -217,7 +217,8 @@ void __dev_map_insert_ctx(struct bpf_map *map, u32 bit) 
}



static int bq_xmit_all(struct bpf_dtab_netdev *obj,

		       struct xdp_bulk_queue *bq, u32 flags)

		       struct xdp_bulk_queue *bq, u32 flags,

		       bool in_napi_ctx)

{

	struct net_device *dev = obj->dev;

	int sent = 0, drops = 0, err = 0;
@@ -254,7 +255,10 @@ static int bq_xmit_all(struct bpf_dtab_netdev *obj, 
		struct xdp_frame *xdpf = bq->q[i];



		/* RX path under NAPI protection, can return frames faster */

		if (likely(in_napi_ctx))

			xdp_return_frame_rx_napi(xdpf);

		else

			xdp_return_frame(xdpf);

		drops++;

	}

	goto out;
@@ -286,7 +290,7 @@ void __dev_map_flush(struct bpf_map *map) 
		__clear_bit(bit, bitmap);



		bq = this_cpu_ptr(dev->bulkq);

		bq_xmit_all(dev, bq, XDP_XMIT_FLUSH);

		bq_xmit_all(dev, bq, XDP_XMIT_FLUSH, true);

	}

}
@@ -316,7 +320,7 @@ static int bq_enqueue(struct bpf_dtab_netdev *obj, struct xdp_frame *xdpf, 
	struct xdp_bulk_queue *bq = this_cpu_ptr(obj->bulkq);



	if (unlikely(bq->count == DEV_MAP_BULK_SIZE))

		bq_xmit_all(obj, bq, 0);

		bq_xmit_all(obj, bq, 0, true);



	/* Ingress dev_rx will be the same for all xdp_frame's in

	 * bulk_queue, because bq stored per-CPU and must be flushed
@@ -385,7 +389,7 @@ static void dev_map_flush_old(struct bpf_dtab_netdev *dev) 
			__clear_bit(dev->bit, bitmap);



			bq = per_cpu_ptr(dev->bulkq, cpu);

			bq_xmit_all(dev, bq, XDP_XMIT_FLUSH);

			bq_xmit_all(dev, bq, XDP_XMIT_FLUSH, false);

		}

	}

}

samples/bpf/xdp_redirect_cpu_kern.c

+1 −1
Original line number Diff line number Diff line
@@ -14,7 +14,7 @@ 
#include <uapi/linux/bpf.h>

#include "bpf_helpers.h"



#define MAX_CPUS 12 /* WARNING - sync with _user.c */

#define MAX_CPUS 64 /* WARNING - sync with _user.c */



/* Special map type that can XDP_REDIRECT frames to another CPU */

struct bpf_map_def SEC("maps") cpu_map = {

samples/bpf/xdp_redirect_cpu_user.c

+2 −2
Original line number Diff line number Diff line
@@ -19,7 +19,7 @@ static const char *__doc__ = 
#include <arpa/inet.h>

#include <linux/if_link.h>



#define MAX_CPUS 12 /* WARNING - sync with _kern.c */

#define MAX_CPUS 64 /* WARNING - sync with _kern.c */



/* How many xdp_progs are defined in _kern.c */

#define MAX_PROG 5
@@ -527,7 +527,7 @@ static void stress_cpumap(void) 
	 * procedure.

	 */

	create_cpu_entry(1,  1024, 0, false);

	create_cpu_entry(1,   128, 0, false);

	create_cpu_entry(1,     8, 0, false);

	create_cpu_entry(1, 16000, 0, false);

}