This is a note to let you know that I've just added the patch titled
mm/filemap: fix page end in filemap_get_read_batch
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-filemap-fix-page-end-in-filemap_get_read_batch.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 5956592ce337330cdff0399a6f8b6a5aea397a8e Mon Sep 17 00:00:00 2001
From: Qian Yingjin <qian@xxxxxxx>
Date: Wed, 8 Feb 2023 10:24:00 +0800
Subject: mm/filemap: fix page end in filemap_get_read_batch
From: Qian Yingjin <qian@xxxxxxx>
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@xxxxxxx
Fixes: cbd59c48ae2b ("mm/filemap: use head pages in generic_file_buffered_read")
Signed-off-by: Qian Yingjin <qian@xxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2538,18 +2538,19 @@ static int filemap_get_pages(struct kioc
struct page *page;
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, pvec);
+ filemap_get_read_batch(mapping, index, last_index - 1, pvec);
if (!pagevec_count(pvec)) {
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, pvec);
+ filemap_get_read_batch(mapping, index, last_index - 1, pvec);
}
if (!pagevec_count(pvec)) {
if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
Patches currently in stable-queue which might be from qian@xxxxxxx are
queue-5.15/mm-filemap-fix-page-end-in-filemap_get_read_batch.patch
