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Date: Tue, 22 Sep 2020 15:35:59 +0100 From: Matthew Wilcox <willy@...radead.org> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Nick Piggin <npiggin@...e.de>, Hugh Dickins <hughd@...gle.com>, Peter Zijlstra <peterz@...radead.org>, Daisuke Nishimura <nishimura@....nes.nec.co.jp>, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] page_alloc: Fix freeing non-compound pages On Tue, Sep 22, 2020 at 03:00:17PM +0100, Matthew Wilcox (Oracle) wrote: > void __free_pages(struct page *page, unsigned int order) > { > if (put_page_testzero(page)) > free_the_page(page, order); > + else > + while (order-- > 0) > + free_the_page(page + (1 << order), order); > } > EXPORT_SYMBOL(__free_pages); ... a three line patch and one of them is wrong. - else + else if (!PageHead(page)) Anyone got a smart idea about how to _test_ this code path? I'm wondering about loading one kernel module which wanders through memmap calling if (page_cache_get_speculative(page)) put_page(page); and another kernel module that calls __free_pages(alloc_page(GFP_KERNEL, 1), 1); and putting in a printk to let me know when we hit it.
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