linux-kernel - Re: [PATCH] fs: prevent data-race due to missing inode_lock when calling vfs

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Message-ID: <20241117165540.GF3387508@ZenIV>
Date: Sun, 17 Nov 2024 16:55:40 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Jeongjun Park <aha310510@...il.com>
Cc: brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] fs: prevent data-race due to missing inode_lock when
 calling vfs_getattr

On Mon, Nov 18, 2024 at 01:37:19AM +0900, Jeongjun Park wrote:
> Many filesystems lock inodes before calling vfs_getattr, so there is no
> data-race for inodes. However, some functions in fs/stat.c that call
> vfs_getattr do not lock inodes, so the data-race occurs.
> 
> Therefore, we need to apply a patch to remove the long-standing data-race
> for inodes in some functions that do not lock inodes.

Why do we care?  Slapping even a shared lock on a _very_ hot path, with
possible considerable latency, would need more than "theoretically it's
a data race".