linux-kernel - Re: [PATCH 2/2] kernfs: dont take i

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Message-ID: <5fd7f78e-4b8f-1dd4-5b3c-e2c3583b9e9d@themaw.net>
Date:   Tue, 1 Nov 2022 16:09:25 +0800
From:   Ian Kent <raven@...maw.net>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, Minchan Kim <minchan@...nel.org>,
        Eric Sandeen <sandeen@...deen.net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Rick Lindsley <ricklind@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] kernfs: dont take i_lock on revalidate


On 1/11/22 15:46, Amir Goldstein wrote:
> On Tue, Oct 18, 2022 at 5:58 AM Ian Kent <raven@...maw.net> wrote:
>> In kernfs_dop_revalidate() when the passed in dentry is negative the
>> dentry directory is checked to see if it has changed and if so the
>> negative dentry is discarded so it can refreshed. During this check
>> the dentry inode i_lock is taken to mitigate against a possible
>> concurrent rename.
>>
>> But if it's racing with a rename, becuase the dentry is negative, it
>> can't be the source it must be the target and it must be going to do
>> a d_move() otherwise the rename will return an error.
>>
>> In this case the parent dentry of the target will not change, it will
>> be the same over the d_move(), only the source dentry parent may change
>> so the inode i_lock isn't needed.
> You meant d_lock.
> Same for the commit title.

Ha, well how do you like that, such an obvious mistake, how

did I not see it?


Not sure what to do about it now though ...

Any suggestions anyone?


Ian