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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Ivan Babrou' <ivan@cloudflare.com>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kernel-team@cloudflare.com" <kernel-team@cloudflare.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Theodore Ts'o <tytso@mit.edu>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        "Johannes Weiner" <hannes@cmpxchg.org>,
        Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        Mike Rapoport <rppt@kernel.org>,
        Yang Shi <shy828301@gmail.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        "Kalesh Singh" <kaleshsingh@google.com>
Subject: RE: [PATCH] proc: report open files as size in stat() for
 /proc/pid/fd
Thread-Topic: [PATCH] proc: report open files as size in stat() for
 /proc/pid/fd
Thread-Index: AQHYzSSDXSMkKVoMw0SOfcp9+NyhuK3prOsw
Date:   Wed, 21 Sep 2022 10:21:24 +0000
Message-ID: <b6aa0151527a4ee39ae85dfd34e71864@AcuMS.aculab.com>
References: <20220920190617.2539-1-ivan@cloudflare.com>
In-Reply-To: <20220920190617.2539-1-ivan@cloudflare.com>
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From: Ivan Babrou
> Sent: 20 September 2022 20:06
...
> 
> +static int proc_readfd_count(struct inode *inode)
> +{
> +	struct task_struct *p = get_proc_task(inode);
> +	struct fdtable *fdt;
> +	unsigned int i, size, open_fds = 0;
> +
> +	if (!p)
> +		return -ENOENT;
> +
> +	if (p->files) {
> +		fdt = files_fdtable(p->files);
> +		size = fdt->max_fds;
> +
> +		for (i = size / BITS_PER_LONG; i > 0;)
> +			open_fds += hweight64(fdt->open_fds[--i]);
> +	}
> +
> +	return open_fds;
> +}
> +

Doesn't that need (at least) rcu protection?
There might also be issues reading p->files twice.

	David

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