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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rhDaF-00000002BSZ-0YnU; Mon, 04 Mar 2024 19:02:43 +0000 Date: Mon, 4 Mar 2024 19:02:43 +0000 From: Matthew Wilcox To: Ryan Roberts Cc: Andrew Morton , linux-mm@kvack.org, Aishwarya TCV , Mark Brown , Ard Biesheuvel Subject: Re: [PATCH 4/8] mm: Add __dump_folio() Message-ID: References: <20240227192337.757313-1-willy@infradead.org> <20240227192337.757313-5-willy@infradead.org> <6de0d026-cd8d-4152-97ca-d33d2a4e2e84@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: ftn64rtpy48nwyccz9i5arg6qcr89atb X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 133FEA002E X-HE-Tag: 1709578965-965113 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Further testing revealed some more problems. We were getting confused between various different pointers leading to spurious messages about the page not matching the folio and passing the wrong pointer to __dump_folio(). Here's a fix-3 patch which I tested like so: +static int __init page_dump(void) +{ + struct page *page; + + printk("testing page dump\n"); + + page = alloc_page(GFP_KERNEL); + dump_page(page, "single"); + put_page(page); + page = alloc_pages(GFP_KERNEL | __GFP_COMP, 2); + dump_page(page, "head"); + dump_page(page + 1, "tail 1"); + dump_page(page + 2, "tail 2"); + dump_page(page + 3, "tail 3"); + put_page(page); + + return 0; +} + +module_init(page_dump); (needed some extra debug to check the values of the pointers being passed to __dump_folio() which we wouldn't want to include) --- mm/debug.c | 36 ++++++++++++++++++++++-------------- 1 file changed, 22 insertions(+), 14 deletions(-) diff --git a/mm/debug.c b/mm/debug.c index e7aa8a9d5d86..4dae73bc4530 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -121,23 +121,31 @@ static void __dump_page(const struct page *page) again: memcpy(&precise, page, sizeof(*page)); foliop = page_folio(&precise); - idx = folio_page_idx(foliop, page); - if (idx != 0) { - if (idx < MAX_FOLIO_NR_PAGES) { - memcpy(&folio, foliop, 2 * sizeof(struct page)); - nr_pages = folio_nr_pages(&folio); - } + if (foliop == (struct folio *)&precise) { + idx = 0; + if (!folio_test_large(foliop)) + goto dump; + foliop = (struct folio *)page; + } else { + idx = folio_page_idx(foliop, page); + } - if (idx > nr_pages) { - if (loops-- > 0) - goto again; - printk("page does not match folio\n"); - precise.compound_head &= ~1UL; - foliop = (struct folio *)&precise; - idx = 0; - } + if (idx < MAX_FOLIO_NR_PAGES) { + memcpy(&folio, foliop, 2 * sizeof(struct page)); + nr_pages = folio_nr_pages(&folio); + foliop = &folio; + } + + if (idx > nr_pages) { + if (loops-- > 0) + goto again; + printk("page does not match folio\n"); + precise.compound_head &= ~1UL; + foliop = (struct folio *)&precise; + idx = 0; } +dump: __dump_folio(foliop, &precise, pfn, idx); } -- 2.43.0