Commit 184cee51 authored by OGAWA Hirofumi's avatar OGAWA Hirofumi Committed by Linus Torvalds
Browse files

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: 0060ef3b ("mm: support THPs in zero_user_segments")
Signed-off-by: default avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4eae4efa

mm/highmem.c

+12 −5
Original line number Diff line number Diff line
@@ -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;

		}