mm: make page pfmemalloc check more robust

Commit c48a11c7ad26 ("netvm: propagate page->pfmemalloc to skb") added
checks for page->pfmemalloc to __skb_fill_page_desc():

        if (page->pfmemalloc && !page->mapping)
                skb->pfmemalloc = true;

It assumes page->mapping == NULL implies that page->pfmemalloc can be
trusted.  However, __delete_from_page_cache() can set set page->mapping
to NULL and leave page->index value alone.  Due to being in union, a
non-zero page->index will be interpreted as true page->pfmemalloc.

So the assumption is invalid if the networking code can see such a page.
And it seems it can.  We have encountered this with a NFS over loopback
setup when such a page is attached to a new skbuf.  There is no copying
going on in this case so the page confuses __skb_fill_page_desc which
interprets the index as pfmemalloc flag and the network stack drops
packets that have been allocated using the reserves unless they are to
be queued on sockets handling the swapping which is the case here and
that leads to hangs when the nfs client waits for a response from the
server which has been dropped and thus never arrive.

The struct page is already heavily packed so rather than finding another
hole to put it in, let's do a trick instead.  We can reuse the index
again but define it to an impossible value (-1UL).  This is the page
index so it should never see the value that large.  Replace all direct
users of page->pfmemalloc by page_is_pfmemalloc which will hide this
nastiness from unspoiled eyes.

The information will get lost if somebody wants to use page->index
obviously but that was the case before and the original code expected
that the information should be persisted somewhere else if that is
really needed (e.g.  what SLAB and SLUB do).

[akpm@linux-foundation.org: fix blooper in slub]
Fixes: c48a11c7ad26 ("netvm: propagate page->pfmemalloc to skb")
Signed-off-by: Michal Hocko <mhocko@suse.com>
Debugged-by: Vlastimil Babka <vbabka@suse.com>
Debugged-by: Jiri Bohac <jbohac@suse.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David Miller <davem@davemloft.net>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: <stable@vger.kernel.org>	[3.6+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 4 insertions, 4 deletions

diff --git a/drivers/net/ethernet/intel/fm10k/fm10k_main.c b/drivers/net/ethernet/intel/fm10k/fm10k_main.c
index 982fdcdc795b..b5b2925103ec 100644
--- a/drivers/net/ethernet/intel/fm10k/fm10k_main.c
+++ b/drivers/net/ethernet/intel/fm10k/fm10k_main.c
@@ -216,7 +216,7 @@ static void fm10k_reuse_rx_page(struct fm10k_ring *rx_ring,
 
 static inline bool fm10k_page_is_reserved(struct page *page)
 {
-	return (page_to_nid(page) != numa_mem_id()) || page->pfmemalloc;
+	return (page_to_nid(page) != numa_mem_id()) || page_is_pfmemalloc(page);
 }
 
 static bool fm10k_can_reuse_rx_page(struct fm10k_rx_buffer *rx_buffer,
diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index 2f70a9b152bd..830466c49987 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -6566,7 +6566,7 @@ static void igb_reuse_rx_page(struct igb_ring *rx_ring,
 
 static inline bool igb_page_is_reserved(struct page *page)
 {
-	return (page_to_nid(page) != numa_mem_id()) || page->pfmemalloc;
+	return (page_to_nid(page) != numa_mem_id()) || page_is_pfmemalloc(page);
 }
 
 static bool igb_can_reuse_rx_page(struct igb_rx_buffer *rx_buffer,
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 9aa6104e34ea..ae21e0b06c3a 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -1832,7 +1832,7 @@ static void ixgbe_reuse_rx_page(struct ixgbe_ring *rx_ring,
 
 static inline bool ixgbe_page_is_reserved(struct page *page)
 {
-	return (page_to_nid(page) != numa_mem_id()) || page->pfmemalloc;
+	return (page_to_nid(page) != numa_mem_id()) || page_is_pfmemalloc(page);
 }
 
 /**
diff --git a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
index e71cdde9cb01..1d7b00b038a2 100644
--- a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
+++ b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
@@ -765,7 +765,7 @@ static void ixgbevf_reuse_rx_page(struct ixgbevf_ring *rx_ring,
 
 static inline bool ixgbevf_page_is_reserved(struct page *page)
 {
-	return (page_to_nid(page) != numa_mem_id()) || page->pfmemalloc;
+	return (page_to_nid(page) != numa_mem_id()) || page_is_pfmemalloc(page);
 }
 
 /**