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Date: Fri, 10 Nov 2023 17:09:27 +0000 From: Matthew Wilcox <willy@...radead.org> To: Andreas Gruenbacher <agruenba@...hat.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-ext4@...r.kernel.org, gfs2@...ts.linux.dev, linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org, "Darrick J . Wong" <djwong@...nel.org>, linux-erofs@...ts.ozlabs.org, Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca> Subject: Re: [PATCH 2/3] mm: Add folio_fill_tail() and use it in iomap On Thu, Nov 09, 2023 at 10:50:45PM +0100, Andreas Gruenbacher wrote: > On Tue, Nov 7, 2023 at 10:27 PM Matthew Wilcox (Oracle) > <willy@...radead.org> wrote: > > +static inline void folio_fill_tail(struct folio *folio, size_t offset, > > + const char *from, size_t len) > > +{ > > + char *to = kmap_local_folio(folio, offset); > > + > > + VM_BUG_ON(offset + len > folio_size(folio)); > > + > > + if (folio_test_highmem(folio)) { > > + size_t max = PAGE_SIZE - offset_in_page(offset); > > + > > + while (len > max) { > > + memcpy(to, from, max); > > + kunmap_local(to); > > + len -= max; > > + from += max; > > + offset += max; > > + max = PAGE_SIZE; > > + to = kmap_local_folio(folio, offset); > > + } > > + } > > + > > + memcpy(to, from, len); > > + to = folio_zero_tail(folio, offset, to); > > This needs to be: > > to = folio_zero_tail(folio, offset + len, to + len); Oh, wow, that was stupid of me. I only ran an xfstests against ext4, which doesn't exercise this code, not gfs2 or erofs. Thanks for fixing this up. I was wondering about adding the assertion: VM_BUG_ON((kaddr - offset) % PAGE_SIZE); to catch the possible mistake of calling kmap_local_folio(folio, 0) instead of kmap_local_folio(folio, offset). But maybe that's sufficiently unlikely a mistake to bother adding a runtime check for.
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