On 09/02/2015 10:41 AM, Dmitry Vyukov wrote: > On Wed, Sep 2, 2015 at 4:18 PM, Peter Hurley <pe...@hurleysoftware.com> wrote: >> On 09/01/2015 04:11 PM, Dmitry Vyukov wrote: >>> The data race is found with KernelThreadSanitizer (on rev 21bdb584af8c): >>> >>> ThreadSanitizer: data-race in release_tty >>> Write of size 8 by thread T325 (K2579): >>> release_tty+0xf3/0x1c0 drivers/tty/tty_io.c:1688 >>> tty_release+0x698/0x7c0 drivers/tty/tty_io.c:1920 >>> __fput+0x15f/0x310 fs/file_table.c:207 >>> ____fput+0x1d/0x30 fs/file_table.c:243 >>> task_work_run+0x115/0x130 kernel/task_work.c:123 >>> do_notify_resume+0x73/0x80 >>> tracehook_notify_resume include/linux/tracehook.h:190 >>> do_notify_resume+0x73/0x80 arch/x86/kernel/signal.c:757 >>> int_signal+0x12/0x17 arch/x86/entry/entry_64.S:326 >>> Previous read of size 8 by thread T19 (K16): >>> flush_to_ldisc+0x29/0x300 drivers/tty/tty_buffer.c:472 >>> process_one_work+0x47e/0x930 kernel/workqueue.c:2036 >>> worker_thread+0xb0/0x900 kernel/workqueue.c:2170 >>> kthread+0x150/0x170 kernel/kthread.c:207 >>> >>> flush_to_ldisc reads port->itty and checks that it is not NULL, >>> concurrently release_tty sets port->itty to NULL. It is possible >>> that flush_to_ldisc loads port->itty once, ensures that it is >>> not NULL, but then reloads it again and uses. The second load >>> can already return NULL, which will cause a crash. >>> >>> Set port->itty to NULL after shutting down flush_to_ldisc work. >>> >>> Signed-off-by: Dmitry Vyukov <dvyu...@google.com> >>> --- >>> drivers/tty/tty_io.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c >>> index 57fc6ee..0df24c1 100644 >>> --- a/drivers/tty/tty_io.c >>> +++ b/drivers/tty/tty_io.c >>> @@ -1684,9 +1684,9 @@ static void release_tty(struct tty_struct *tty, int >>> idx) >>> tty_free_termios(tty); >>> tty_driver_remove_tty(tty->driver, tty); >>> tty->port->itty = NULL; >>> + cancel_work_sync(&tty->port->buf.work); >>> if (tty->link) >>> tty->link->port->itty = NULL; >>> - cancel_work_sync(&tty->port->buf.work); >> >> This patch doesn't do anything. > > It sets tty->link->port->itty to NULL _after_ waiting for > flush_to_ldisc work to finish. At least this is the intention. > Can you explain why it does not do anything?
Because tty->link is a different tty than that corresponding to the buffer work being cancelled. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
