On Fri, Jan 08, 2010 at 10:15:10PM +0900, Tetsuo Handa wrote: > Dave Chinner wrote: > > On Fri, Jan 08, 2010 at 11:54:24AM +0900, Tetsuo Handa wrote: > > > I'm experiencing file corruption problem. > > > Can somebody reproduce below result? > > > > > > My environment: > > > VMware Workstation 6.5.3 with 2CPUs / 512MB RAM. > > > ext3 filesystem ( /dev/sda1 ) mounted on / . > > > > > > 2.6.33-rc3 ( http://I-love.SAKURA.ne.jp/tmp/config-2.6.33-rc3-ext3 ) > > > 2.6.32.3 ( http://I-love.SAKURA.ne.jp/tmp/config-2.6.32.3-ext3 ) > > > 2.6.31.11 ( http://I-love.SAKURA.ne.jp/tmp/config-2.6.31.11-ext3 ) > > > 2.6.30.10 > > > > > > So far, I haven't succeeded to reproduce this problem for 2.6.29 and earlier. > > > Maybe this problem exists in only 2.6.30 and later. > > > > Isn't that when the default mount options changed from data=ordered to > > data=writeback? > Ah, indeed. 2.6.31 mounts data=writeback whereas 2.6.29 mounts data=ordered. > > In my Ubuntu 9.10 environment, it is using data=writeback mode, and therefore > I got garbage data taken from other deleted files. > > > You didn't fsync() it, so there is no reason for the kernel > > to have ever written it to disk. Therefore the result after powerfail > > is completely undefined - you data may be there, it may not... > > I didn't call fsync(). Thus, I don't mind if the data I wrote is not written > to disk. Ok, I was making sure you weren't misunderstanding what the fflush() is supposed to guarantee - many people do, but you're not one of them :) > However, I feel something is very wrong because the file got data which I > didn't write. The file gets data from deleted files. Imagine that unprivileged > user can get the content of /etc/shadow if power failure occurred when the user > was running ./a.out . Ah, so it was stale data you were seeing. > The file should not get data from deleted files, but I can read the data from > deleted files by "cat /testfile". I feel something is very wrong. I agree that it is very wrong, but it's a known problem with writeback mode in ext3: http://thread.gmane.org/gmane.linux.kernel/818044/focus=819977 More info as to how this change came about and the proposed but not yet realised fixes: http://lwn.net/Articles/328363/ Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
