[PATCH] bounce:fix bug, avoid to flush dcache on slab page from jbd2.

[Shuge]

The bounce accept slab pages from jbd2, and flush dcache on them.
When enabling VM_DEBUG, it will tigger VM_BUG_ON in page_mapping().
So, check PageSlab to avoid it in __blk_queue_bounce().

Bug URL: http://lkml.org/lkml/2013/3/7/56

Signed-off-by: shuge <shuge@xxxxxxxxxxxxxxxxx>
---
 mm/bounce.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/bounce.c b/mm/bounce.c
index 4e9ae72..f352c03 100644
--- a/mm/bounce.c
+++ b/mm/bounce.c
@@ -214,7 +214,8 @@ static void __blk_queue_bounce(struct request_queue 
*q, struct bio **bio_orig,
 		if (rw == WRITE) {
 			char *vto, *vfrom;
 -			flush_dcache_page(from->bv_page);
+			if (unlikely(!PageSlab(from->bv_page)))
+				flush_dcache_page(from->bv_page);
 			vto = page_address(to->bv_page) + to->bv_offset;
 			vfrom = kmap(from->bv_page) + from->bv_offset;
 			memcpy(vto, vfrom, to->bv_len);
--
1.7.9.5

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