From 184cee516f3e24019a08ac8eb5c7cf04c00933cb Mon Sep 17 00:00:00 2001 From: OGAWA Hirofumi Date: Fri, 12 Mar 2021 21:07:37 -0800 Subject: mm/highmem.c: fix zero_user_segments() with start > end zero_user_segments() is used from __block_write_begin_int(), for example like the following zero_user_segments(page, 4096, 1024, 512, 918) But new the zero_user_segments() implementation for for HIGHMEM + TRANSPARENT_HUGEPAGE doesn't handle "start > end" case correctly, and hits BUG_ON(). (we can fix __block_write_begin_int() instead though, it is the old and multiple usage) Also it calls kmap_atomic() unnecessarily while start == end == 0. Link: https://lkml.kernel.org/r/87v9ab60r4.fsf@mail.parknet.co.jp Fixes: 0060ef3b4e6d ("mm: support THPs in zero_user_segments") Signed-off-by: OGAWA Hirofumi Cc: Matthew Wilcox Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/highmem.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/mm/highmem.c b/mm/highmem.c index 874b732b120c..86f2b9495f9c 100644 --- a/mm/highmem.c +++ b/mm/highmem.c @@ -368,20 +368,24 @@ void zero_user_segments(struct page *page, unsigned start1, unsigned end1, BUG_ON(end1 > page_size(page) || end2 > page_size(page)); + if (start1 >= end1) + start1 = end1 = 0; + if (start2 >= end2) + start2 = end2 = 0; + for (i = 0; i < compound_nr(page); i++) { void *kaddr = NULL; - if (start1 < PAGE_SIZE || start2 < PAGE_SIZE) - kaddr = kmap_atomic(page + i); - if (start1 >= PAGE_SIZE) { start1 -= PAGE_SIZE; end1 -= PAGE_SIZE; } else { unsigned this_end = min_t(unsigned, end1, PAGE_SIZE); - if (end1 > start1) + if (end1 > start1) { + kaddr = kmap_atomic(page + i); memset(kaddr + start1, 0, this_end - start1); + } end1 -= this_end; start1 = 0; } @@ -392,8 +396,11 @@ void zero_user_segments(struct page *page, unsigned start1, unsigned end1, } else { unsigned this_end = min_t(unsigned, end2, PAGE_SIZE); - if (end2 > start2) + if (end2 > start2) { + if (!kaddr) + kaddr = kmap_atomic(page + i); memset(kaddr + start2, 0, this_end - start2); + } end2 -= this_end; start2 = 0; } -- cgit v1.2.3