I recently found a bug introduced in your commit
65500d234e74fc4e8f18e1a429bc24e51e75de4a, i.e. between 2.6.14 and 2.6.15-rc1,
about do_file_page changes wrt remap_file_pages and MAP_POPULATE.
Quoting from the changelog (which is wrong):
do_file_page's fallback to do_no_page dates from a time when we were
testing
pte_file by using it wherever possible: currently it's peculiar to
nonlinear
vmas, so just check that. BUG_ON if not? Better not, it's probably page
table corruption, so just show the pte: hmm, there's a pte_ERROR macro,
let's
use that for do_wp_page's invalid pfn too.
This is false:
do_mmap_pgoff:
if (flags & MAP_POPULATE) {
up_write(&mm->mmap_sem);
sys_remap_file_pages(addr, len, 0,
pgoff, flags & MAP_NONBLOCK);
down_write(&mm->mmap_sem);
}
So, with MAP_POPULATE|MAP_NONBLOCK passed, you can get a linear PAGE_FILE pte
in a !VM_NONLINEAR vma.
That PTE is very useless since it doesn't add any information, I know that, so
avoiding that possible installation is a possible fix, but for now it's
simpler to change the test in do_file_page(). Btw, in fact I discovered this
bug while I was implementing this optimization (working again on
remap_file_pages() patches of this summer).
Indeed, the condition to test (and to possibly BUG_ON/pte_ERROR) is that
->populate must exist for the sys_remap_file_pages call to work.
--
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade
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