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Date:   Fri, 6 Oct 2023 15:21:30 +0200
From:   Mateusz Guzik <mjguzik@gmail.com>
To:     Sven Schnelle <svens@linux.ibm.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"
Message-ID: <20231006132130.bpekoewcsjqz4qps@f>
References: <00e5cc23-a888-46ce-8789-fc182a2131b0@sirena.org.uk>
 <yt9dil7k151d.fsf@linux.ibm.com>
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 <yt9d4jj3zzbn.fsf@linux.ibm.com>
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On Fri, Oct 06, 2023 at 02:54:04PM +0200, Sven Schnelle wrote:
> 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.

so i wrote this as an immediate fixup. not the prettiest, but should
prevent the need to drop the patch from linux-next.

diff --git a/fs/file.c b/fs/file.c
index 2f6965848907..8d62d6f46982 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -1024,7 +1024,7 @@ static inline struct file *files_lookup_fdget_rcu(struct files_struct *files, un
 {
 	RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
 			 "suspicious rcu_dereference_check() usage");
-	return lookup_fdget_rcu(fd);
+	return __fget_files_rcu(files, fd, 0);
 }
 
 struct file *task_lookup_fdget_rcu(struct task_struct *task, unsigned int fd)