Commit 35b7a191 authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'net-drivers-pgcnt' 



Eric Dumazet says:

====================
net: fix races accessing page->_count

This is illegal to use atomic_set(&page->_count, ...) even if we 'own'
the page. Other entities in the kernel need to use get_page_unless_zero()
to get a reference to the page before testing page properties, so we could
loose a refcount increment.

The only case it is valid is when page->_count is 0, we can use this in
__netdev_alloc_frag()

Note that I never seen crashes caused by these races, the issue was reported
by Andres Lagar-Cavilla and Hugh Dickins.
====================

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents 1fadee0c 4c450583

drivers/net/ethernet/intel/fm10k/fm10k_main.c

+3 −4
Original line number Diff line number Diff line
@@ -219,11 +219,10 @@ static bool fm10k_can_reuse_rx_page(struct fm10k_rx_buffer *rx_buffer, 
	/* flip page offset to other buffer */

	rx_buffer->page_offset ^= FM10K_RX_BUFSZ;



	/* since we are the only owner of the page and we need to

	 * increment it, just set the value to 2 in order to avoid

	 * an unnecessary locked operation

	/* Even if we own the page, we are not allowed to use atomic_set()

	 * This would break get_page_unless_zero() users.

	 */

	atomic_set(&page->_count, 2);

	atomic_inc(&page->_count);

#else

	/* move offset up to the next cache line */

	rx_buffer->page_offset += truesize;

drivers/net/ethernet/intel/igb/igb_main.c

+3 −4
Original line number Diff line number Diff line
@@ -6545,11 +6545,10 @@ static bool igb_can_reuse_rx_page(struct igb_rx_buffer *rx_buffer, 
	/* flip page offset to other buffer */

	rx_buffer->page_offset ^= IGB_RX_BUFSZ;



	/* since we are the only owner of the page and we need to

	 * increment it, just set the value to 2 in order to avoid

	 * an unnecessary locked operation

	/* Even if we own the page, we are not allowed to use atomic_set()

	 * This would break get_page_unless_zero() users.

	 */

	atomic_set(&page->_count, 2);

	atomic_inc(&page->_count);

#else

	/* move offset up to the next cache line */

	rx_buffer->page_offset += truesize;

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

+3 −5
Original line number Diff line number Diff line
@@ -1865,12 +1865,10 @@ static bool ixgbe_add_rx_frag(struct ixgbe_ring *rx_ring, 
	/* flip page offset to other buffer */

	rx_buffer->page_offset ^= truesize;



	/*

	 * since we are the only owner of the page and we need to

	 * increment it, just set the value to 2 in order to avoid

	 * an unecessary locked operation

	/* Even if we own the page, we are not allowed to use atomic_set()

	 * This would break get_page_unless_zero() users.

	 */

	atomic_set(&page->_count, 2);

	atomic_inc(&page->_count);

#else

	/* move offset up to the next cache line */

	rx_buffer->page_offset += truesize;

drivers/net/ethernet/mellanox/mlx4/en_rx.c

+3 −3
Original line number Diff line number Diff line
@@ -76,10 +76,10 @@ static int mlx4_alloc_pages(struct mlx4_en_priv *priv, 
	page_alloc->dma = dma;

	page_alloc->page_offset = frag_info->frag_align;

	/* Not doing get_page() for each frag is a big win

	 * on asymetric workloads.

	 * on asymetric workloads. Note we can not use atomic_set().

	 */

	atomic_set(&page->_count,

		   page_alloc->page_size / frag_info->frag_stride);

	atomic_add(page_alloc->page_size / frag_info->frag_stride - 1,

		   &page->_count);

	return 0;

}

net/core/skbuff.c

+18 −7
Original line number Diff line number Diff line
@@ -360,18 +360,29 @@ refill: 
				goto end;

		}

		nc->frag.size = PAGE_SIZE << order;

recycle:

		atomic_set(&nc->frag.page->_count, NETDEV_PAGECNT_MAX_BIAS);

		/* Even if we own the page, we do not use atomic_set().

		 * This would break get_page_unless_zero() users.

		 */

		atomic_add(NETDEV_PAGECNT_MAX_BIAS - 1,

			   &nc->frag.page->_count);

		nc->pagecnt_bias = NETDEV_PAGECNT_MAX_BIAS;

		nc->frag.offset = 0;

	}



	if (nc->frag.offset + fragsz > nc->frag.size) {

		/* avoid unnecessary locked operations if possible */

		if ((atomic_read(&nc->frag.page->_count) == nc->pagecnt_bias) ||

		    atomic_sub_and_test(nc->pagecnt_bias, &nc->frag.page->_count))

			goto recycle;

		if (atomic_read(&nc->frag.page->_count) != nc->pagecnt_bias) {

			if (!atomic_sub_and_test(nc->pagecnt_bias,

						 &nc->frag.page->_count))

				goto refill;

			/* OK, page count is 0, we can safely set it */

			atomic_set(&nc->frag.page->_count,

				   NETDEV_PAGECNT_MAX_BIAS);

		} else {

			atomic_add(NETDEV_PAGECNT_MAX_BIAS - nc->pagecnt_bias,

				   &nc->frag.page->_count);

		}

		nc->pagecnt_bias = NETDEV_PAGECNT_MAX_BIAS;

		nc->frag.offset = 0;

	}



	data = page_address(nc->frag.page) + nc->frag.offset;

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