linux-kernel - Re: [PATCH tip/core/rcu 07/13] vfs: apply lockdep-based checking to rcu

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Date:	Sun, 14 Feb 2010 11:12:10 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH tip/core/rcu 07/13] vfs: apply lockdep-based checking
 to rcu_dereference() uses

On Thu, 2010-02-11 at 16:00 -0800, Paul E. McKenney wrote:
> 
> -#define files_fdtable(files) (rcu_dereference((files)->fdt))
> +#define files_fdtable(files) \
> +       (rcu_dereference_check((files)->fdt, \
> +                              rcu_read_lock_held() || \
> +                              lockdep_is_held(&(files)->file_lock) ||
> \
> +                              atomic_read(&files->count) == 1))
>  
>  struct file_operations;
>  struct vfsmount;
> @@ -78,7 +82,7 @@ static inline struct file * fcheck_files(struct files_struct *files, unsigned in
>         struct fdtable *fdt = files_fdtable(files);
>  
>         if (fd < fdt->max_fds)
> -               file = rcu_dereference(fdt->fd[fd]);
> +               file = rcu_dereference_check(fdt->fd[fd], rcu_read_lock_held() || lockdep_is_held(&files->file_lock) || atomic_read(&files->count) == 1);
>         return file; 

I'm almost thinking you can do something smart here and not replicate
that condition :-)


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