[to-be-updated] mm-filemap-annotate-lockless-reads-of-mapping-nrpages.patch removed from -mm tree

[to-be-updated] mm-filemap-annotate-lockless-reads-of-mapping-nrpages.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/filemap: annotate lockless reads of mapping->nrpages
has been removed from the -mm tree.  Its filename was
     mm-filemap-annotate-lockless-reads-of-mapping-nrpages.patch

This patch was dropped because an updated version will be issued

------------------------------------------------------
From: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>
Subject: mm/filemap: annotate lockless reads of mapping->nrpages
Date: Mon, 12 Oct 2026 21:39:21 +0700

mapping->nrpages is updated under the i_pages lock but is read locklessly
as a cheap "anything cached?" hint, e.g.  in invalidate_bdev() and
filemap_write_and_wait_range().  KCSAN reports the race:

  BUG: KCSAN: data-race in __filemap_add_folio / invalidate_bdev

  read-write to 0xffff8881004c4178 of 8 bytes by task 3600 on cpu 0:
   __filemap_add_folio+0x6b7/0x910 mm/filemap.c:919
   filemap_add_folio+0x1cd/0x380
   page_cache_ra_unbounded+0x1a4/0x3a0
   ...
   blkdev_read_iter+0x21e/0x2d0
  read to 0xffff8881004c4178 of 8 bytes by task 3601 on cpu 1:
   invalidate_bdev+0x25/0x70 block/bdev.c:98
   ext4_fill_super+0x2ccb/0x37b0

The same counter also races with filemap_write_and_wait_range() through
mapping_needs_writeback().

The race is benign: a stale value only makes the caller do or skip a
harmless invalidate/flush pass.  Mark the lockless reads with data_race()
in invalidate_bdev() and in the two callers of mapping_needs_writeback(),
rather than inside the helper, so a future user needing a reliable answer
is not silently covered.

Link: https://lore.kernel.org/20261012143921.283806-1-ngocthang2710.1999@gmail.com
Signed-off-by: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: <syzbot+e0624b5bf72b99131402@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=e0624b5bf72b99131402
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
---

 block/bdev.c |    3 ++-
 mm/filemap.c |    6 ++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

--- a/block/bdev.c~mm-filemap-annotate-lockless-reads-of-mapping-nrpages
+++ a/block/bdev.c
@@ -95,7 +95,8 @@ void invalidate_bdev(struct block_device
 {
 	struct address_space *mapping = bdev->bd_mapping;
 
-	if (mapping->nrpages) {
+	/* Lockless hint; a stale value only costs or skips a harmless pass */
+	if (data_race(mapping->nrpages)) {
 		invalidate_bh_lrus();
 		lru_add_drain_all();	/* make sure all lru add caches are flushed */
 		invalidate_mapping_pages(mapping, 0, -1);
--- a/mm/filemap.c~mm-filemap-annotate-lockless-reads-of-mapping-nrpages
+++ a/mm/filemap.c
@@ -680,7 +680,8 @@ int filemap_write_and_wait_range(struct
 	if (lend < lstart)
 		return 0;
 
-	if (mapping_needs_writeback(mapping)) {
+	/* Lockless hint; a stale value is harmless */
+	if (data_race(mapping_needs_writeback(mapping))) {
 		err = filemap_fdatawrite_range(mapping, lstart, lend);
 		/*
 		 * Even if the above returned error, the pages may be
@@ -782,7 +783,8 @@ int file_write_and_wait_range(struct fil
 	if (lend < lstart)
 		return 0;
 
-	if (mapping_needs_writeback(mapping)) {
+	/* Lockless hint; a stale value is harmless */
+	if (data_race(mapping_needs_writeback(mapping))) {
 		err = filemap_fdatawrite_range(mapping, lstart, lend);
 		/* See comment of filemap_write_and_wait() */
 		if (err != -EIO)
_

Patches currently in -mm which might be from ngocthang2710.1999@gmail.com are