block: blk_max_pfn is somtimes wrong
There is a small problem in handling page bounce.
At the moment blk_max_pfn equals max_pfn, which is in fact not maximum
possible _number_ of a page frame, but the _amount_ of page frames. For
example for the 32bit x86 node with 4Gb RAM, max_pfn = 0x100000, but not
0xFFFF.
request_queue structure has a member q->bounce_pfn and queue needs bounce
pages for the pages _above_ this limit. This routine is handled by
blk_queue_bounce(), where the following check is produced:
if (q->bounce_pfn >= blk_max_pfn)
return;
Assume, that a driver has set q->bounce_pfn to 0xFFFF, but blk_max_pfn
equals 0x10000. In such situation the check above fails and for each bio
we always fall down for iterating over pages tied to the bio.
I want to notice, that for quite a big range of device drivers (ide, md,
...) such problem doesn't happen because they use BLK_BOUNCE_ANY for
bounce_pfn. BLK_BOUNCE_ANY is defined as blk_max_pfn << PAGE_SHIFT, and
then the check above doesn't fail. But for other drivers, which obtain
reuired value from drivers, it fails. For example sata_nv uses
ATA_DMA_MASK or dev->dma_mask.
I propose to use (max_pfn - 1) for blk_max_pfn. And the same for
blk_max_low_pfn. The patch also cleanses some checks related with
bounce_pfn.
Signed-off-by: Vasily Tarasov <vtaras@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 38c293b..3de0695 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -1221,7 +1221,7 @@
* considered part of another segment, since that might
* change with the bounce page.
*/
- high = page_to_pfn(bv->bv_page) >= q->bounce_pfn;
+ high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
if (high || highprv)
goto new_hw_segment;
if (cluster) {
@@ -3658,8 +3658,8 @@
open_softirq(BLOCK_SOFTIRQ, blk_done_softirq, NULL);
register_hotcpu_notifier(&blk_cpu_notifier);
- blk_max_low_pfn = max_low_pfn;
- blk_max_pfn = max_pfn;
+ blk_max_low_pfn = max_low_pfn - 1;
+ blk_max_pfn = max_pfn - 1;
return 0;
}
