On 06/10/2013 05:31 PM, Dave Chinner wrote: > On Mon, Jun 10, 2013 at 09:17:31AM -0400, Brian Foster wrote: >> Hi guys, >> >> I wanted to get this onto the list... I suspect this could be >> similar/related to the issue reported here: >> >> http://oss.sgi.com/archives/xfs/2013-06/msg00066.html > > Unlikely - generic/263 tests mmap IO vs direct IO, and Sage's > problem has neither... > Oh, Ok. I didn't look at that one closely enough then. >> While running xfstests, the only apparent regression I hit from 3.9.0 >> was generic/263. This test fails due to the following command (and >> resulting output): > > Not a regression - 263 has been failing ever since it was introduced > in 2011 by: > > commit 0d69e10ed15b01397e8c6fd7833fa3c2970ec024 ... > > It is testing mmap() writes vs direct IO, something that is known to > be fundamentally broken (i.e. racy) as mmap() page fault path does > not hold the XFS_IOLOCK or i_mutex in any way. The direct IO path > tries to wark around this by flushing and invalidating cached pages > before IO submission, but the lack of locking in the page fault path > means we can't avoid the race entirely. > Thanks for the explanation. >> P.S., I also came across the following thread which, if related, >> suggests this might be known/understood to a degree: >> >> http://oss.sgi.com/archives/xfs/2012-04/msg00703.html > > Yup, that's potentially one aspect of it. However, have you run the > test code on ext3/4? it works just fine - it's only XFS that has > problems with this case, so it's not clear that this is a DIO > problem. It was never able to work out where ext3/ext4 were zeroing > the part of the page beyond EOF, and I couldn't ever make the DIO > code reliably do the right thing. It's one of the reasons that lead > to this discussion as LSFMM: > > http://lwn.net/Articles/548351/ > Interesting, thanks again. I did happen to run the script and the fsx test on the ext4 rootfs of my VM and observed expected behavior. Note that I mentioned this was harder to reproduce with fixed alloc sizes less than 128k or so. I don't believe ext4 does any kind of speculative preallocation in the manner that XFS does. Perhaps that is a factor..? Brian > Cheers, > > Dave. > _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
