linux-kernel - [PATCH 0/2] ubifs: Fixes for xattr concurrent operations

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Date:   Mon, 31 May 2021 20:52:08 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     <richard@....at>, <yangds.fnst@...fujitsu.com>,
        <s.hauer@...gutronix.de>
CC:     <yi.zhang@...wei.com>, <houtao1@...wei.com>, <yukuai3@...wei.com>,
        <chengzhihao1@...wei.com>, <linux-mtd@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 0/2] ubifs: Fixes for xattr concurrent operations

UBIFS may occur some problems with concurrent xattr_{set|get} and
listxattr operations, such as assertion failure, memory corruption,
stale xattr value[1].

Patch 1: Import a new rw-lock in @ubifs_inode to serilize write
	 operations on xattr
Patch 2: Remove unnecessary ui_mutex in ubifs_xattr_get and change_xattr

BTW changing @host->ui_mutex to a rw lock to adapting xattr operations
is a risky method, since @host->ui_mutex acts as too many roles:
* serializes inode write-back with the rest of VFS operations(such as
  rename, mkdir, rmdir, create, eg.)
* serializes "clean <-> dirty" state changes, serializes bulk-read
* protects @dirty, @bulk_read, @ui_size, and @xattr_size

Besides, if xattr operations and io/vfs operations share same rw-lock,
xattr operations may effect UBIFS performance more or less.

[1] https://lore.kernel.org/linux-mtd/20200630130438.141649-1-houtao1@huawei.com

Zhihao Cheng (2):
  ubifs: Fix races between xattr_{set|get} and listxattr operations
  ubifs: Remove ui_mutex in ubifs_xattr_get and change_xattr

 fs/ubifs/super.c |  1 +
 fs/ubifs/ubifs.h |  2 ++
 fs/ubifs/xattr.c | 48 +++++++++++++++++++++++++++++++++---------------
 3 files changed, 36 insertions(+), 15 deletions(-)

-- 
2.25.4