| From | Peter Hurley <> | Subject | [PATCH v2 08/14] tty: Convert tty_struct bitfield to ints | Date | Wed, 10 Sep 2014 15:06:30 -0400 |
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The stopped, hw_stopped, flow_stopped and packet bits are smp-unsafe and interrupt-unsafe. For example,
CPU 0 | CPU 1 | tty->flow_stopped = 1 | tty->hw_stopped = 0
One of these updates will be corrupted, as the bitwise operation on the bitfield is non-atomic.
Ensure each flag has a separate memory location, so concurrent updates do not corrupt orthogonal states. Because DEC Alpha EV4 and EV5 cpus (from 1995) perform RMW on smaller-than-machine-word storage, "separate memory location" must be int instead of byte.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com> --- include/linux/tty.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/include/linux/tty.h b/include/linux/tty.h index 1c3316a..a707196 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -261,7 +261,10 @@ struct tty_struct { unsigned long flags; int count; struct winsize winsize; /* winsize_mutex */ - unsigned char stopped:1, hw_stopped:1, flow_stopped:1, packet:1; + int stopped; + int flow_stopped; + int hw_stopped; + int packet; unsigned char ctrl_status; /* ctrl_lock */ unsigned int receive_room; /* Bytes free for queue */ int flow_change; -- 2.1.0
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