4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Matthew Wilcox (Oracle) willy@infradead.org
commit 1b151e2435fc3a9b10c8946c6aebe9f3e1938c55 upstream.
The special casing was originally added in pre-git history; reproducing the commit log here:
commit a318a92567d77 Author: Andrew Morton akpm@osdl.org 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: stable@vger.kernel.org Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/bio.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
--- 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 *b 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; }