tty: fix data race between tty_init_dev and flush of buf
There can be a race, if receive_buf call comes before tty initialization completes in n_tty_open and tty->disc_data may be NULL. CPU0 CPU1 ---- ---- 000|n_tty_receive_buf_common() n_tty_open() -001|n_tty_receive_buf2() tty_ldisc_open.isra.3() -002|tty_ldisc_receive_buf(inline) tty_ldisc_setup() Using ldisc semaphore lock in tty_init_dev till disc_data initializes completely. Signed-off-by: NGaurav Kohli <gkohli@codeaurora.org> Reviewed-by: NAlan Cox <alan@linux.intel.com> Cc: stable <stable@vger.kernel.org> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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