On Wed, Oct 15, 2008 at 10:19:44AM +0200, Richard Kojedzinszky wrote: > dear nick, > > i have tried a sync after the remount, but that did not help. what helped > is dropping the cache by echoing 3 to /proc/sys/vm/drop_caches, but this > still didnt solve the problem in 100%, only in 95% of the cases. > > But when i read the device with > # dd if=/dev/ram0 iflag=direct ... > then it worked. I think this bypassed some caches, and thus read the > actual data. > > But a sad result is that I experienced with it, and only with ramdisk does > it work as expected. for example with a logical volume it behaves in the > wrong way. I've reproduced this problem (ext2 image corruption flagged in e2fsck even though it was remounted ro and marked clean in the sb). Issuing a sync, then drop_caches, seems to fix it here for me. On the other hand, I also see problems with inconsistencies even after unmounting if I hold the /dev/ram0 device open with something else (which causes the buffer cache not to be invalidated on unmount). I think what is happening is that the block device is being modified without going through the buffer cache (ie. via pagecache or direct writes), but the buffer cache doesn't get invalidated. So you get stale data when reading from /dev/ram0. I don't think we're going to want the overhead in the kernel to detect these kinds of aliases. It might be reasonable to flush the blockdev on unmount and remount,ro after syncing the filesystem. The old rd driver's backing store was actually its buffercache, so that particular issue wouldn't cause aliasing. Thanks, Nick -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
