fs/buffer.c: add checking buffer head stat before clear

mainline inclusion
from mainline-v5.11-rc3
commit 4ebd3aec
category: bugfix
bugzilla: 175148
CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4ebd3aec3842662300979dacd6fb38e3e8edf7f4

------------------------------------------------------------------------

clear_buffer_new() is used to clear buffer new stat.  When PAGE_SIZE is
64K, most buffer heads in the list are not needed to clear.
clear_buffer_new() has an enpensive atomic modification operation, Let's
add checking buffer head before clear it as __block_write_begin_int does
which is good for performance.

Link: https://lkml.kernel.org/r/1612332890-57918-1-git-send-email-zhangshaokun@hisilicon.comSigned-off-by: NYang Guo <guoyang2@huawei.com>
Signed-off-by: NShaokun Zhang <zhangshaokun@hisilicon.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: NShaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/buffer.c

@@ -2083,7 +2083,8 @@ static int __block_commit_write(struct inode *inode, struct page *page,
 			set_buffer_uptodate(bh);
 			mark_buffer_dirty(bh);
 		}
-		clear_buffer_new(bh);
+		if (buffer_new(bh))
+			clear_buffer_new(bh);
 
 		block_start = block_end;
 		bh = bh->b_this_page;