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Message-ID: <87zgzq89nf.fsf@mail.parknet.co.jp> Date: Sat, 27 Feb 2021 12:36:04 +0900 From: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> To: Matthew Wilcox <willy@...radead.org> Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH] Fix zero_user_segments() with start > end Matthew Wilcox <willy@...radead.org> writes: > On Sat, Feb 27, 2021 at 01:11:35AM +0900, OGAWA Hirofumi wrote: >> 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 zero_user_segments() implements for HIGMEM + 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) > > Why don't we just take out the BUG_ON instead? The function doesn't > actually do the wrong thing. end1 is underflow with if (start1 >= PAGE_SIZE) { start1 -= PAGE_SIZE; end1 -= PAGE_SIZE; } >> Also it calls kmap_atomic() unnecessary while start == end == 0. > > I'm OK with that. It always used to do that. Old one is only one page, so it is always necessary if start1/end1 or start2/end2 is valid range. But this one is multiple pages, so there are completely unnecessary pages possibly. >> Cc: <stable@...r.kernel.org> >> Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> > > Fixes: 0060ef3b4e6d ("mm: support THPs in zero_user_segments") OK. -- OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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