linux-kernel - Re: [PATCH v2 4/7] fsnotify: skip unattached marks

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Date:   Mon, 30 Oct 2017 15:27:06 +0100
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Amir Goldstein <amir73il@...il.com>,
        Xiong Zhou <xzhou@...hat.com>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/7] fsnotify: skip unattached marks

On Mon, Oct 30, 2017 at 3:00 PM, Jan Kara <jack@...e.cz> wrote:
> On Wed 25-10-17 10:41:36, Miklos Szeredi wrote:
>> After having gone through a ref-unref for the mark, dereferencing the group
>> (e.g. in fsnotify_compare_groups()) is wrong since the group may be
>> completely gone by that time.  So before continuing to traverse the mark
>> list, check if the mark is still attached.
>
> Are you sure this can happen? The thing is: Group reference from mark is
> dropped only in fsnotify_final_mark_destroy(). That gets called after SRCU
> period is finished from fsnotify_mark_destroy_workfn(). And SRCU period in
> which we have dropped our mark reference in fsnotify_finish_user_wait() has
> not yet ended. What am I missing?

Ah, missed that fact that mark holds a ref on the group until it's destroyed.

Yes, the patch is unnecessary in this case.

Thanks,
Miklos