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From:   Sven Schnelle <svens@linux.ibm.com>
To:     Mateusz Guzik <mjguzik@gmail.com>
Cc:     Mark Brown <broonie@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Jann Horn <jannh@google.com>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: Test failure from "file: convert to SLAB_TYPESAFE_BY_RCU"
References: <00e5cc23-a888-46ce-8789-fc182a2131b0@sirena.org.uk>
        <yt9dil7k151d.fsf@linux.ibm.com> <ZR//+QDRI3sBpqY4@f>
Date:   Fri, 06 Oct 2023 14:54:04 +0200
In-Reply-To: <ZR//+QDRI3sBpqY4@f> (Mateusz Guzik's message of "Fri, 6 Oct 2023
        14:39:21 +0200")
Message-ID: <yt9d4jj3zzbn.fsf@linux.ibm.com>
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Mateusz Guzik <mjguzik@gmail.com> writes:

> On Fri, Oct 06, 2023 at 11:19:58AM +0200, Sven Schnelle wrote:
>> I'm seeing the same with the strace test-suite on s390. The problem is
>> that /proc/*/fd now contains the file descriptors of the calling
>> process, and not the target process.
>> 
>
> This is why:
>
> +static inline struct file *files_lookup_fdget_rcu(struct files_struct *files, unsigned int fd)
> +{
> +       RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
> +                        "suspicious rcu_dereference_check() usage");
> +       return lookup_fdget_rcu(fd);
> +}
>
> files argument is now thrown away, instead it always uses current.

Yes, passing files to lookup_fdget_rcu() fixes the issue.