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From:   =?UTF-8?q?Joan=20Bruguera=20Mic=C3=B3?= <joanbrugueram@gmail.com>
To:     zhengqi.arch@bytedance.com
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <roman.gushchin@linux.dev>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: shrinkers: fix race condition on debugfs cleanup
Date:   Sun, 21 May 2023 13:57:33 +0000
Message-Id: <20230521135733.1076395-1-joanbrugueram@gmail.com>
In-Reply-To: <2d44a1bd-eb80-7724-ff4e-a0fc3bfd8b72@bytedance.com>
References: <2d44a1bd-eb80-7724-ff4e-a0fc3bfd8b72@bytedance.com>
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On 2023/5/3 13:37, Qi Zheng wrote:
> > +void shrinker_debugfs_remove(struct dentry *debugfs_entry, int debugfs_id)
> > +{
> 
> It would be better to add a check:
> 
> 	if (!debugfs_entry)
> 		return;
> 
> > +	debugfs_remove_recursive(debugfs_entry);
> > +	ida_free(&shrinker_debugfs_ida, debugfs_id);
> > +}

As a practical matter, both `debugfs_remove_recursive(NULL)` and
`ida_free(_, -1);` are documented as no-ops, see:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/debugfs/inode.c?id=0dd2a6fb1e34d6dcb96806bc6b111388ad324722#n748
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fc82bbf4dede758007763867d0282353c06d1121

Sorry for the late reply (the patch already reached the mainline tree).