Messages in this thread | | | Date | Tue, 15 Jul 2008 13:18:40 +1000 | From | Dave Chinner <> | Subject | Re: xfs bug in 2.6.26-rc9 |
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On Tue, Jul 15, 2008 at 12:12:52PM +1000, Lachlan McIlroy wrote: > Dave Chinner wrote: >> On Mon, Jul 14, 2008 at 05:34:51PM +1000, Lachlan McIlroy wrote: >>> This is a race between xfs_fsr and a mmap write. xfs_fsr acquires the >>> iolock and then flushes the file and because it has the iolock it doesn't >>> expect any new delayed allocations to occur. A mmap write can allocate >>> delayed allocations without acquiring the iolock so is able to get in >>> after the flush but before the ASSERT. >> >> Christoph and I were contemplating this problem with ->page_mkwrite >> reecently. The problem is that we can't, right now, return an >> EAGAIN-like error to ->page_mkwrite() and have it retry the >> page fault. Other parts of the page faulting code can do this, >> so it seems like a solvable problem. >> >> The basic concept is that if we can return a EAGAIN result we can >> try-lock the inode and hold the locks necessary to avoid this race >> or prevent the page fault from dirtying the page until the >> filesystem is unfrozen. > Why do we need to try-lock the inode? Will we have an ABBA deadlock > if we block on the iolock in ->page_mkwrite()?
Yes. With the mmap_sem. Look at the rules in mm/filemap.c and replace i_mutex with iolock....
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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