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 <redacted>
---
  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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