On 08. 05. 24, 11:30, kovalev@altlinux.org wrote:
From: Vasiliy Kovalev kovalev@altlinux.org
A possible scenario in which a deadlock may occur is as follows:
flush_to_ldisc() {
mutex_lock(&buf->lock);
tty_port_default_receive_buf() { tty_ldisc_receive_buf() { n_tty_receive_buf2() { n_tty_receive_buf_common() { n_tty_receive_char_special() { isig() { tty_driver_flush_buffer() { pty_flush_buffer() { tty_buffer_flush() {
mutex_lock(&buf->lock); (DEADLOCK)flush_to_ldisc() and tty_buffer_flush() functions they use the same mutex (&buf->lock), but not necessarily the same struct tty_bufhead object.
"not necessarily" -- so does it mean that it actually can happen (and we should fix it) or not at all (and we should annotate the mutex)?
However, you should probably use a separate mutex for the tty_buffer_flush() function to exclude such a situation.
...
Cc: stable@vger.kernel.org
What commit does this fix?
--- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -226,7 +226,7 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld) atomic_inc(&buf->priority);
- mutex_lock(&buf->lock);
- mutex_lock(&buf->flush_mtx);
Hmm, how does this protect against concurrent buf pickup. We free it here and the racing thread can start using it, or?
/* paired w/ release in __tty_buffer_request_room; ensures there are * no pending memory accesses to the freed buffer */
thanks,