FAILED: patch "[PATCH] mm/filemap: fix page end in filemap_get_read_batch" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Possible dependencies:

5956592ce337 ("mm/filemap: fix page end in filemap_get_read_batch") 25d6a23e8d28 ("filemap: Convert filemap_get_read_batch() to use a folio_batch") d996fc7f615f ("filemap: Convert filemap_read() to use a folio") 65bca53b5f63 ("filemap: Convert filemap_get_pages to use folios") a5d4ad098528 ("filemap: Convert filemap_create_page to folio") 9d427b4eb456 ("filemap: Convert filemap_read_page to take a folio") bdb729329769 ("filemap: Convert filemap_get_read_batch to use folios") 512b7931ad05 ("Merge branch 'akpm' (patches from Andrew)")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

Quoted 1 line

From 5956592ce337330cdff0399a6f8b6a5aea397a8e Mon Sep 17 00:00:00 2001

From: Qian Yingjin <[email protected]>
Date: Wed, 8 Feb 2023 10:24:00 +0800
Subject: [PATCH] mm/filemap: fix page end in filemap_get_read_batch

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/[email protected] open here

Fixes cbd59c48ae2b ("mm/filemap: use head pages in generic_file_buffered_read")

Signed-off-by Qian Yingjin <[email protected]>

Reviewed-by Matthew Wilcox (Oracle) <[email protected]>

Cc <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

mm/filemap.c +3 -2

index c4d4ace9cc70..0e20a8d6dd93 100644
@@ -2588,18 +2588,19 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
 	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))

Quoted 5 lines · On Sat, Feb 18, 2023 at 09:02:42AM +0100, [email protected] wrote:

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Here's a patch for 5.15-stable, generated against v5.15.94