[PATCH] secretmem: optimize page_is_secretmem()
willy at infradead.org
Mon Apr 19 12:23:02 BST 2021
On Mon, Apr 19, 2021 at 11:42:18AM +0300, Mike Rapoport wrote:
> The perf profile of the test indicated that the regression is caused by
> page_is_secretmem() called from gup_pte_range() (inlined by gup_pgd_range):
Uhh ... you're calling it in the wrong place!
page = pte_page(pte);
head = try_grab_compound_head(page, 1, flags);
So you're calling page_is_secretmem() on a struct page without having
a refcount on it. That is definitely not allowed. secretmem seems to
be full of these kinds of races; I know this isn't the first one I've
seen in it. I don't think this patchset is ready for this merge window.
With that fixed, you'll have a head page that you can use for testing,
which means you don't need to test PageCompound() (because you know the
page isn't PageTail), you can just test PageHead().
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