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SubjectRe: [PATCH] fs: avoid unecessary smp_wmb() in dup_fd()
On Sat, May 07, 2011 at 08:30:01AM +0200, Eric Dumazet wrote:
> While copying old_fds array to new_fds, we dont need
> rcu_assign_pointer() and its smp_wmb(), since we are the only thread
> populating new_fds at this point.
>
> A bit later, rcu_assign_pointer(newf->fdt, new_fdt) makes sure
> our writes are committed to memory before new_fds content is visible to
> other threads.
>
> This removes following sparse warning :
>
> fs/file.c:371:3: warning: incorrect type in assignment (different
> address spaces)
> fs/file.c:371:3: expected struct file *<noident>
> fs/file.c:371:3: got struct file [noderef] <asn:4>*<noident>

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Matthew Wilcox <matthew@wil.cx>
> Cc: linux-fsdevel@vger.kernel.org
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Changli Gao <xiaosuo@gmail.com>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
> fs/file.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/file.c b/fs/file.c
> index 4c6992d..8320a8e 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -368,7 +368,7 @@ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
> */
> FD_CLR(open_files - i, new_fdt->open_fds);
> }
> - rcu_assign_pointer(*new_fds++, f);
> + *new_fds++ = f;
> }
> spin_unlock(&oldf->file_lock);
>
>
>


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