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. Use READ_ONCE/WRITE_ONCE to read/update port->itty. Signed-off-by: Dmitry Vyukov <dvyu...@google.com> --- drivers/tty/tty_buffer.c | 2 +- drivers/tty/tty_io.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index 4cf263d..1f1031d 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -469,7 +469,7 @@ static void flush_to_ldisc(struct work_struct *work) struct tty_struct *tty; struct tty_ldisc *disc; - tty = port->itty; + tty = READ_ONCE(port->itty); if (tty == NULL) return; diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 57fc6ee..aad47df 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1685,7 +1685,7 @@ static void release_tty(struct tty_struct *tty, int idx) tty_driver_remove_tty(tty->driver, tty); tty->port->itty = NULL; if (tty->link) - tty->link->port->itty = NULL; + WRITE_ONCE(tty->link->port->itty, NULL); cancel_work_sync(&tty->port->buf.work); tty_kref_put(tty->link); -- 2.5.0.457.gab17608 -- 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/