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Message-ID: <17976.43884.191895.235227@zeus.sw.starentnetworks.com>
Date: Wed, 2 May 2007 11:17:00 -0400
From: Dave Johnson <djohnson+linux-kernel@...starentnetworks.com>
To: linux-kernel@...r.kernel.org
Subject: do_tty_write() can block even with O_NONBLOCK?
I have two processes with the same tty open, one opens blocking and
one opens nonblocking.
If the blocking process blocks doing a write (due to flow control,
just going to fast, etc...) the nonblocking process will also block
when it writes until the blocking process unblocks.
This seems to occur because do_tty_write() isn't checking for
O_NONBLOCK when taking the tty's write mutex.
Signed-off-by: Dave Johnson <djohnson+linux-kernel@...starentnetworks.com>
===== drivers/char/tty_io.c 1.237 vs edited =====
--- 1.237/drivers/char/tty_io.c 2007-03-18 16:40:06 -04:00
+++ edited/drivers/char/tty_io.c 2007-05-01 10:53:27 -04:00
@@ -1690,9 +1690,13 @@
ssize_t ret = 0, written = 0;
unsigned int chunk;
- /* FIXME: O_NDELAY ... */
- if (mutex_lock_interruptible(&tty->atomic_write_lock)) {
- return -ERESTARTSYS;
+ if (file->f_flags & O_NONBLOCK) {
+ if (!mutex_trylock(&tty->atomic_write_lock))
+ return -EAGAIN;
+ }
+ else {
+ if (mutex_lock_interruptible(&tty->atomic_write_lock))
+ return -ERESTARTSYS;
}
/*
-
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