Messages in this thread | | | Date | Wed, 14 May 2003 11:53:19 -0700 | From | Andrew Morton <> | Subject | Re: Race between vmtruncate and mapped areas? |
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Dave McCracken <dmccr@us.ibm.com> wrote: > > > --On Wednesday, May 14, 2003 11:17:48 -0700 Andrew Morton <akpm@digeo.com> > wrote: > > > I think it might be sufficient to re-check the page against i_size > > after IO completion in filemap_nopage(). > > It would definitely make the window a lot smaller, though it won't quite > close it. To be entirely safe we'd need to recheck after we've retaken > page_table_lock.
hmm.
One possible timing diagram is
truncate: pagefault:
check i_size
grab page drop i_size
shoot down pagetables
install in pagetables
truncate file
converting i_sem to an rwsem and taking it in the pagefault would certainly stitch it up. Unpopular, very messy.
Could "truncate file" return some code to say pages were left behind, so truncate re-runs zap_page_range()? Sounds unpleasant.
Yes, re-checking the page against i_size from do_no_page() would fix it up. But damn, that's another indirect call, 64-bit math, etc on _every_ file-backed pagefault.
Remind me again what problem this whole thing is currently causing?
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