From 7cad96ae59b334a80b6e48c396f147a6c810c9ea Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Mon, 8 Sep 2025 11:45:17 +0200 Subject: [PATCH] mm/gup: fix handling of errors from arch_make_folio_accessible() in follow_page_pte() In case we call arch_make_folio_accessible() and it fails, we would incorrectly return a value that is "!= 0" to the caller, indicating that we pinned all requested pages and that the caller can keep going. follow_page_pte() is not supposed to return error values, but instead "0" on failure and "1" on success -- we'll clean that up separately. In case we return "!= 0", the caller will just keep going pinning more pages. If we happen to pin a page afterwards, we're in trouble, because we essentially skipped some pages in the requested range. Staring at the arch_make_folio_accessible() implementation on s390x, I assume it should actually never really fail unless something unexpected happens (BUG?). So let's not CC stable and just fix common code to do the right thing. Clean up the code a bit now that there is no reason to store the return value of arch_make_folio_accessible(). Link: https://lkml.kernel.org/r/20250908094517.303409-1-david@redhat.com Fixes: f28d43636d6f ("mm/gup/writeback: add callbacks for inaccessible pages") Signed-off-by: David Hildenbrand Reviewed-by: Claudio Imbrenda Cc: Jason Gunthorpe Cc: John Hubbard Cc: Peter Xu Cc: Christian Borntraeger Signed-off-by: Andrew Morton --- mm/gup.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 00f30e03f736..a8ba5112e4d0 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2898,12 +2898,9 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr, * see Documentation/core-api/pin_user_pages.rst for * details. */ - if (flags & FOLL_PIN) { - ret = arch_make_folio_accessible(folio); - if (ret) { - gup_put_folio(folio, 1, flags); - goto pte_unmap; - } + if ((flags & FOLL_PIN) && arch_make_folio_accessible(folio)) { + gup_put_folio(folio, 1, flags); + goto pte_unmap; } folio_set_referenced(folio); pages[*nr] = page;