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Subject[PATCH] Remove useless memory barrier.
I don't see why there is a memory barrier in copy_from_read_buf() at all.
Even if it was useful spin_unlock_irqrestore implies a barrier.

Signed-off-by: Ralf Baechle <>

diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c
index 603b9ad..8df7ff3 100644
--- a/drivers/char/n_tty.c
+++ b/drivers/char/n_tty.c
@@ -1151,7 +1151,6 @@ static int copy_from_read_buf(struct tty
n = min(*nr, n);
spin_unlock_irqrestore(&tty->read_lock, flags);
if (n) {
- mb();
retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
n -= retval;
spin_lock_irqsave(&tty->read_lock, flags);
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