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author | Nitin Gupta <ngupta@vflare.org> | 2009-10-12 14:20:23 +0530 |
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committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2009-10-12 17:52:26 +0100 |
commit | 787b2faadc4356b6c2c71feb42fb944fece9a12f (patch) | |
tree | e3acab624bb2de248a2e4f1e6293024200c8dc8c /fs/sysfs | |
parent | edc72786d208e77db94f84dcb0d166c0d23d82f7 (diff) | |
download | op-kernel-dev-787b2faadc4356b6c2c71feb42fb944fece9a12f.zip op-kernel-dev-787b2faadc4356b6c2c71feb42fb944fece9a12f.tar.gz |
ARM: force dcache flush if dcache_dirty bit set
On ARM, update_mmu_cache() does dcache flush for a page only if
it has a kernel mapping (page_mapping(page) != NULL). The correct
behavior would be to force the flush based on dcache_dirty bit only.
One of the cases where present logic would be a problem is when
a RAM based block device[1] is used as a swap disk. In this case,
we would have in-memory data corruption as shown in steps below:
do_swap_page()
{
- Allocate a new page (if not already in swap cache)
- Issue read from swap disk
- Block driver issues flush_dcache_page()
- flush_dcache_page() simply sets PG_dcache_dirty bit and does not
actually issue a flush since this page has no user space mapping yet.
- Now, if swap disk is almost full, this newly read page is removed
from swap cache and corrsponding swap slot is freed.
- Map this page anonymously in user space.
- update_mmu_cache()
- Since this page does not have kernel mapping (its not in page/swap
cache and is mapped anonymously), it does not issue dcache flush
even if dcache_dirty bit is set by flush_dcache_page() above.
<user now gets stale data since dcache was never flushed>
}
Same problem exists on mips too.
[1] example:
- brd (RAM based block device)
- ramzswap (RAM based compressed swap device)
Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'fs/sysfs')
0 files changed, 0 insertions, 0 deletions