From: Qian Yingjin qian@ddn.com
commit 5956592ce337330cdff0399a6f8b6a5aea397a8e upstream.
I was running traces of the read code against an RAID storage system to understand why read requests were being misaligned against the underlying RAID strips. I found that the page end offset calculation in filemap_get_read_batch() was off by one.
When a read is submitted with end offset 1048575, then it calculates the end page for read of 256 when it should be 255. "last_index" is the index of the page beyond the end of the read and it should be skipped when get a batch of pages for read in @filemap_get_read_batch().
The below simple patch fixes the problem. This code was introduced in kernel 5.12.
Link: https://lkml.kernel.org/r/20230208022400.28962-1-coolqyj@163.com Fixes: cbd59c48ae2b ("mm/filemap: use head pages in generic_file_buffered_read") Signed-off-by: Qian Yingjin qian@ddn.com Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/filemap.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/mm/filemap.c +++ b/mm/filemap.c @@ -2569,18 +2569,19 @@ static int filemap_get_pages(struct kioc struct folio *folio; int err = 0;
+ /* "last_index" is the index of the page beyond the end of the read */ last_index = DIV_ROUND_UP(iocb->ki_pos + iter->count, PAGE_SIZE); retry: if (fatal_signal_pending(current)) return -EINTR;
- filemap_get_read_batch(mapping, index, last_index, fbatch); + filemap_get_read_batch(mapping, index, last_index - 1, fbatch); if (!folio_batch_count(fbatch)) { if (iocb->ki_flags & IOCB_NOIO) return -EAGAIN; page_cache_sync_readahead(mapping, ra, filp, index, last_index - index); - filemap_get_read_batch(mapping, index, last_index, fbatch); + filemap_get_read_batch(mapping, index, last_index - 1, fbatch); } if (!folio_batch_count(fbatch)) { if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))