On Wed, Dec 08, 2010 at 07:20:24AM -0500, Chris Mason wrote: > Excerpts from Jon Nelson's message of 2010-12-07 22:29:26 -0500: > > On Tue, Dec 7, 2010 at 3:02 PM, Chris Mason <chris.mason@xxxxxxxxxx> wrote: > > > Excerpts from Jon Nelson's message of 2010-12-07 15:48:58 -0500: > > >> On Tue, Dec 7, 2010 at 2:41 PM, Chris Mason <chris.mason@xxxxxxxxxx> wrote: > > >> > Excerpts from Jon Nelson's message of 2010-12-07 15:25:47 -0500: > > >> >> On Tue, Dec 7, 2010 at 2:02 PM, Chris Mason <chris.mason@xxxxxxxxxx> wrote: > > >> >> > Excerpts from Jon Nelson's message of 2010-12-07 14:34:40 -0500: > > >> >> >> On Tue, Dec 7, 2010 at 12:52 PM, Chris Mason <chris.mason@xxxxxxxxxx> wrote: > > >> >> >> >> postgresql errors. Typically, header corruption but from the limited > > >> >> >> >> visibility I've had into this via strace, what I see is zeroed pages > > >> >> >> >> where there shouldn't be. > > >> >> >> > > > >> >> >> > This sounds a lot like a bug higher up than dm-crypt. Zeros tend to > > >> >> >> > come from some piece of code explicitly filling a page with zeros, and > > >> >> >> > that often happens in the corner cases for O_DIRECT and a few other > > >> >> >> > places in the filesystem. > > >> >> >> > > > >> >> >> > Have you tried triggering this with a regular block device? > > >> >> >> > > >> >> >> I just tried the whole set of tests, but with /dev/sdb directly (as > > >> >> >> ext4) without any crypt-y bits. > > >> >> >> It takes more iterations but out of 6 tests I had one failure: same > > >> >> >> type of thing, 'invalid page header in block ....'. > > >> >> >> > > >> >> >> I can't guarantee that it is a full-page of zeroes, just what I saw > > >> >> >> from the (limited) stracing I did. > > >> >> > > > >> >> > Fantastic. Now for our usual suspects: > > > > Maybe not so fantastic. I kept testing and had no more failures. At > > all. After 40+ iterations I gave up. > > I went back to trying ext4 on a LUKS volume. The 'hit' ratio went to > > something like 1 in 3, or better. > > > > I will continue to do testing with and without LUKS. I did /not/ > > reboot between tests, but I do start with a fresh postgres database. > > > > Once we trigger once without dm-crypt, dm-crypt is off the hook. Just > to verify, when you say without luks, you mean without any crypto bits > in use at all on the filesystems postgres uses? > > Usually the trick to reproducing filesystem corruptions is adding memory > pressure. The corruption is probably a bad interaction between reads > and writes, and we need to make sure the reads actually happen. > > http://oss.oracle.com/~mason/pin_ram.c > > gcc -Wall -o pin_ram pin_ram.c > > pin_ram -m 80%-of-your-ram-in-mb Implemented in xfstests about 10 years ago: http://git.kernel.org/?p=fs/xfs/xfstests-dev.git;a=blob;f=src/usemem.c;h=b8794a6b209cebf8dbf312a8ef131e2e54b18d29;hb=HEAD :P Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
