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authorFrancesco Ruggeri <fruggeri@aristanetworks.com>2014-10-10 13:09:53 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-06 12:23:36 -0800
commitc4dc304677e8d566572c4738d95c48be150c6606 (patch)
tree93241c8332a47a765bc8338415c8b9e7996049a0
parent7e12e675c17982a8b3cc91314a68f4c4d1bceb92 (diff)
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tty: Fix pty master poll() after slave closes v2
Commit f95499c3030f ("n_tty: Don't wait for buffer work in read() loop") introduces a race window where a pty master can be signalled that the pty slave was closed before all the data that the slave wrote is delivered. Commit f8747d4a466a ("tty: Fix pty master read() after slave closes") fixed the problem in case of n_tty_read, but the problem still exists for n_tty_poll. This can be seen by running 'for ((i=0; i<100;i++));do ./test.py ;done' where test.py is: import os, select, pty (pid, pty_fd) = pty.fork() if pid == 0: os.write(1, 'This string should be received by parent') else: poller = select.epoll() poller.register( pty_fd, select.EPOLLIN ) ready = poller.poll( 1 * 1000 ) for fd, events in ready: if not events & select.EPOLLIN: print 'missed POLLIN event' else: print os.read(fd, 100) poller.close() The string from the slave is missed several times. This patch takes the same approach as the fix for read and special cases this condition for poll. Tested on 3.16. Signed-off-by: Francesco Ruggeri <fruggeri@arista.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/tty/n_tty.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 89c4cee253e3..2e900a98c3e3 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2413,12 +2413,17 @@ static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file,
poll_wait(file, &tty->read_wait, wait);
poll_wait(file, &tty->write_wait, wait);
+ if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
+ mask |= POLLHUP;
if (input_available_p(tty, 1))
mask |= POLLIN | POLLRDNORM;
+ else if (mask & POLLHUP) {
+ tty_flush_to_ldisc(tty);
+ if (input_available_p(tty, 1))
+ mask |= POLLIN | POLLRDNORM;
+ }
if (tty->packet && tty->link->ctrl_status)
mask |= POLLPRI | POLLIN | POLLRDNORM;
- if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
- mask |= POLLHUP;
if (tty_hung_up_p(file))
mask |= POLLHUP;
if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) {