linux-kernel - Re: [syzbot] [mm?] KCSAN: data-race in generic_fillattr / shmem

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Date:   Mon, 1 May 2023 23:05:35 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     akpm@...ux-foundation.org, hughd@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com,
        syzbot <syzbot+702361cf7e3d95758761@...kaller.appspotmail.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [syzbot] [mm?] KCSAN: data-race in generic_fillattr / shmem_mknod
 (2)

On 2023/05/01 14:15, Tetsuo Handa wrote:
> Hmm, where is the serialization that avoids concurrent
> shmem_mknod()/shmem_mknod() or shmem_mknod()/shmem_unlink() ?
> i_size_write() says "need locking around it (normally i_mutex)"...
> 
Since filename_create() calls inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT)
and done_path_create() calls inode_unlock(path->dentry->d_inode), serialization looks OK.
Just the name is no longer i_mutex ?

> Also, there was a similar report on updating i_{ctime,mtime} to current_time()
> which means that i_size is not the only field that is causing data race.
> https://syzkaller.appspot.com/bug?id=067d40ab9ab23a6fa0a8156857ed54e295062a29

Do we want to as well wrap i_{ctime,mtime} using data_race() ?