linux-kernel - Re: [PATCH v2] cifs: remove unnecessary copies of tcon->crfid.fid

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Message-ID: <8735vp18su.fsf@suse.com>
Date:   Sat, 17 Apr 2021 12:53:37 +0200
From:   Aurélien Aptel <aaptel@...e.com>
To:     Muhammad Usama Anjum <musamaanjum@...il.com>,
        Steve French <sfrench@...ba.org>,
        Ronnie Sahlberg <lsahlber@...hat.com>,
        "open list:COMMON INTERNET FILE SYSTEM CLIENT (CIFS)" 
        <linux-cifs@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Cc:     musamaanjum@...il.com, kernel-janitors@...r.kernel.org,
        dan.carpenter@...cle.com, colin.king@...onical.com
Subject: Re: [PATCH v2] cifs: remove unnecessary copies of tcon->crfid.fid

Hi,

This is better I think.

Muhammad Usama Anjum <musamaanjum@...il.com> writes:
> @@ -894,6 +891,10 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
>  
>  	/* BB TBD check to see if oplock level check can be removed below */
>  	if (o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE) {
> +		/*
> +		 * caller expects this func to set the fid in crfid to valid
> +		 * cached root, so increment the refcount.
> +		 */

This comment is misleading. crfid variable doesn't exist anymore, and
the kref_get() here is because of this commit:

    commit 2f94a3125b87
    Author: Ronnie Sahlberg <lsahlber@...hat.com>
    Date:   Thu Mar 28 11:20:02 2019 +1000
    
        cifs: fix kref underflow in close_shroot()

        [...]
-->     This extra get() is only used to hold the structure until we get a lease
-->     break from the server at which point we will kref_put() it during lease
-->     processing.
        [...]



When we queue a lease break, we usually get() the cifsFileInfo, but if
that cifsFileInfo is backed by a cached_fid, the cached_fid isn't
bumped. That commit was probably a work around for that.

@Ronnie :

struct cached_fid is starting to look very much like struct
cifsFileInfo. I wonder why we couldn't use it, along with
find_writable_file()/find_readable_file() to handle the caching.

Alternatively, make cifsFileInfo use cached_fid (perhaps renaming it in
the process, I don't know)

Because I suspect a lot more issues will come up regarding cached_fid
refcount and cifsFileInfo refcount going out of sync otherwise.

Cheers,
-- 
Aurélien Aptel / SUSE Labs Samba Team
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