linux-kernel - RE: [PATCH RFC 4/4] 9p: fix race issue in fid contention.

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Date:   Fri, 18 Sep 2020 10:05:33 +0000
From:   Jianyong Wu <Jianyong.Wu@....com>
To:     Dominique Martinet <asmadeus@...ewreck.org>
CC:     "ericvh@...il.com" <ericvh@...il.com>,
        "lucho@...kov.net" <lucho@...kov.net>,
        "v9fs-developer@...ts.sourceforge.net" 
        <v9fs-developer@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Justin He <Justin.He@....com>, Greg Kurz <groug@...d.org>
Subject: RE: [PATCH RFC 4/4] 9p: fix race issue in fid contention.



> -----Original Message-----
> From: Dominique Martinet <asmadeus@...ewreck.org>
> Sent: Friday, September 18, 2020 5:35 PM
> To: Jianyong Wu <Jianyong.Wu@....com>
> Cc: ericvh@...il.com; lucho@...kov.net; v9fs-
> developer@...ts.sourceforge.net; linux-kernel@...r.kernel.org; Justin He
> <Justin.He@....com>; Greg Kurz <groug@...d.org>
> Subject: Re: [PATCH RFC 4/4] 9p: fix race issue in fid contention.
>
> Jianyong Wu wrote on Fri, Sep 18, 2020:
> > If we move the counter decrease code into p9_client_clunk and put it
> > instead of fid_atomic_dec, we need delete fid off the inode where it
> > stores in p9_client_clunk.
> > But there is no way can we acquire the inode in p9_client_clunk. Do
> > you have any idea? I think introduce another parameter for
> > p9_client_clunk Is not graceful.
>
> You cannot write code about the inode in p9_client_clunk, the way the code
> is split fs/9p can refer to net/9p but not the other way around (module-wise,
> 9p can refer to 9pnet but 9pnet cannot refer to 9p or we would have cyclic
> dependencies)
>
> However I don't see what bothers you.
> v9fs_dir_release can remove the fid from the inode as it does currently and
> just clunk immediately afterwards.
>
>
> If another user of the fid had gotten the fid from the inode previously, it has
> a ref, so the fid will not be actually clunked then but it will be clunked later
> when it is done being used -- that is perfectly fine ?
>
> p9_client_clunk should not have to worry about anything in the vfs.
>
Yeah, I see. That's it.

Thanks
Jianyong
> --
> Dominique
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