Messages in this thread | | | Date | Fri, 12 Jan 2007 10:05:24 +1100 | From | David Chinner <> | Subject | Re: 2.6.20-rc4: known regressions with patches (v3) |
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On Thu, Jan 11, 2007 at 02:02:41PM -0800, Andrew Morton wrote: > On Fri, 12 Jan 2007 08:39:16 +1100 > David Chinner <dgc@sgi.com> wrote: > > > On Thu, Jan 11, 2007 at 06:13:29AM +0100, Adrian Bunk wrote: > > > This email lists some known regressions in 2.6.20-rc4 compared to 2.6.19 > > > with patches available. > > > > > > Subject : BUG: at mm/truncate.c:60 cancel_dirty_page() (XFS) > > > References : http://lkml.org/lkml/2007/1/5/308 > > > Submitter : Sami Farin <7atbggg02@sneakemail.com> > > > Handled-By : David Chinner <dgc@sgi.com> > > > Patch : http://lkml.org/lkml/2007/1/7/201 > > > Status : patch available > > > > Patch is broken, do not merge. The original had an off-by-one bug in > > it, and the fixed one I have has just shown a worse problem than > > before - partial page truncation (i.e. filesystem block size less > > than page size) is busted because invalidate_complete_page2_range() can > > only handle complete pages. > > > > Andrew - looking at unmap_mapping_pages, it says it cannot handle > > partial pages and must get rid of them whereas vmtrucate() handles > > partial pages but changes file size so can't be used. I see that > > vmtruncate handles this by not unmapping the first partial page. > > > > I can use the vmtruncate mechanism (unmap_mapping_pages, then > > truncate_inode_pages) but that seems racy to me because we are not > > actually truncating the file so a mmap could remap a page between > > the unmap and the truncate and hence we still get the warning. > > Yes, truncate relies upon there being nothing outside i_size, and that > i_mutex is held. > > > So the question is - is there any generic function that handles > > this case (i.e. don't unmap first partial page, unmap the rest, > > partial truncate of first page, complete truncate of the rest) > > without racing? Or do I need to write a variation of > > invalidate_inode_pages2_range() to do this? > > umm, nothing I can immediately think of. Perhaps you can generalise > vmtruncate_range() a bit?
I had a look at that - apart from being used for actually freeing disk blocks as well (punching a hole in the file) - it requires locks that we may or may not be able to grab and still has the problem of separate calls to unmap_mapping_pages and truncate_inode_pages_range.
Unless I'm misunderstanding the purpose of vmtruncate_range() I don't think it's the right API to be using because XFS only needs to invalidate the page cache (hence my thoughts on a variant of invalidate_inode_pages2_range being required).
Am I making sense, or do I need more coffe this morning?
Cheers,
Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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