From d2d0b95ca1b5fefa3deed444a803c9f809db66cf Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Mon, 14 Aug 2023 15:41:00 +0100 Subject: block: Remove special-casing of compound pages commit 1b151e2435fc3a9b10c8946c6aebe9f3e1938c55 upstream. The special casing was originally added in pre-git history; reproducing the commit log here: > commit a318a92567d77 > Author: Andrew Morton > Date: Sun Sep 21 01:42:22 2003 -0700 > > [PATCH] Speed up direct-io hugetlbpage handling > > This patch short-circuits all the direct-io page dirtying logic for > higher-order pages. Without this, we pointlessly bounce BIOs up to > keventd all the time. In the last twenty years, compound pages have become used for more than just hugetlb. Rewrite these functions to operate on folios instead of pages and remove the special case for hugetlbfs; I don't think it's needed any more (and if it is, we can put it back in as a call to folio_test_hugetlb()). This was found by inspection; as far as I can tell, this bug can lead to pages used as the destination of a direct I/O read not being marked as dirty. If those pages are then reclaimed by the MM without being dirtied for some other reason, they won't be written out. Then when they're faulted back in, they will not contain the data they should. It'll take a pretty unusual setup to produce this problem with several races all going the wrong way. This problem predates the folio work; it could for example have been triggered by mmaping a THP in tmpfs and using that as the target of an O_DIRECT read. Fixes: 800d8c63b2e98 ("shmem: add huge pages support") Cc: Signed-off-by: Matthew Wilcox (Oracle) Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/bio.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/block/bio.c b/block/bio.c index 7858b2d23916..476a88e11715 100644 --- a/block/bio.c +++ b/block/bio.c @@ -1592,8 +1592,7 @@ void bio_set_pages_dirty(struct bio *bio) int i; bio_for_each_segment_all(bvec, bio, i) { - if (!PageCompound(bvec->bv_page)) - set_page_dirty_lock(bvec->bv_page); + set_page_dirty_lock(bvec->bv_page); } } EXPORT_SYMBOL_GPL(bio_set_pages_dirty); @@ -1652,7 +1651,7 @@ void bio_check_pages_dirty(struct bio *bio) int i; bio_for_each_segment_all(bvec, bio, i) { - if (!PageDirty(bvec->bv_page) && !PageCompound(bvec->bv_page)) + if (!PageDirty(bvec->bv_page)) goto defer; } -- cgit v1.2.3