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igb: fix race accessing page->_count

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This is illegal to use atomic_set(&page->_count, 2) 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.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2014-10-10 04:48:15 -07:00 committed by David S. Miller
parent 42b0270b40
commit 00cd5adb03
1 changed files with 3 additions and 4 deletions
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7
drivers/net/ethernet/intel/igb/igb_main.c
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@ -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;