linux-kernel - Re: [PATCH] hfsplus: don't use BUG_ON() in hfsplus_create_attributes

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Message-ID: <3efa3d2a-e98f-43ee-91dd-5aeefcff75e1@I-love.SAKURA.ne.jp>
Date: Thu, 10 Jul 2025 07:03:18 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>,
        "frank.li@...o.com" <frank.li@...o.com>,
        "glaubitz@...sik.fu-berlin.de" <glaubitz@...sik.fu-berlin.de>,
        "slava@...eyko.com" <slava@...eyko.com>,
        "brauner@...nel.org" <brauner@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Cc: "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hfsplus: don't use BUG_ON() in
 hfsplus_create_attributes_file()

On 2025/07/10 3:33, Viacheslav Dubeyko wrote:
> My worry that we could have a race condition here. Let's imagine that two
> threads are trying to call __hfsplus_setxattr() and both will try to create the
> Attributes File. Potentially, we could end in situation when inode could have
> not zero size during hfsplus_create_attributes_file() in one thread because
> another thread in the middle of Attributes File creation. Could we double check
> that we don't have the race condition here? Otherwise, we need to make much
> cleaner fix of this issue.

I think that there is some sort of race window, for
https://elixir.bootlin.com/linux/v6.15.5/source/fs/hfsplus/xattr.c#L145
explains that if more than one thread concurrently reached

	if (!HFSPLUS_SB(inode->i_sb)->attr_tree) {
		err = hfsplus_create_attributes_file(inode->i_sb);
		if (unlikely(err))
			goto end_setxattr;
	}

path, all threads except one thread will fail with -EAGAIN.