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mm/highmem.c: fix zero_user_segments() with start > end

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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: 0060ef3b4e ("mm: support THPs in zero_user_segments")
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
OGAWA Hirofumi 2021-03-12 21:07:37 -08:00 committed by Linus Torvalds
parent 4eae4efa2c
commit 184cee516f
1 changed files with 12 additions and 5 deletions
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17
mm/highmem.c
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@ -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;
}