On 11/11/2015 03:35 AM, Dmitry Vyukov wrote:
> Hello,
>
> I've hit the following deadlock while running syzkaller on commit
> ce5c2d2c256a4c8b523036537cd6be2d6af8f69d (Nov 7):
>
> [ INFO: possible circular locking dependency detected ]
> 4.3.0+ #57 Not tainted
> -------------------------------------------------------
> syzkaller_execu/24882 is trying to acquire lock:
> (&tty->atomic_write_lock){+.+.+.}, at: [<ffffffff81774876>]
> tty_write_lock+0x46/0x70 drivers/tty/tty_io.c:1093
>
> but task is already holding lock:
> (&tty->termios_rwsem){++++.+}, at: [<ffffffff817864d7>]
> n_tty_ioctl_helper+0x177/0x210 drivers/tty/tty_ioctl.c:1150
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&tty->termios_rwsem){++++.+}:
> [<ffffffff81122501>] lock_acquire+0x101/0x1d0
> kernel/locking/lockdep.c:3585
> [<ffffffff821727a9>] down_read+0x39/0x50 kernel/locking/rwsem.c:22
> [<ffffffff8177eb07>] n_tty_write+0x137/0xaa0 drivers/tty/n_tty.c:2362
> [< inline >] do_tty_write drivers/tty/tty_io.c:1164
> [<ffffffff8177832e>] tty_write+0x28e/0x4f0 drivers/tty/tty_io.c:1248
> [<ffffffff81778631>] redirected_tty_write+0xa1/0xb0
> drivers/tty/tty_io.c:1269
> [<ffffffff812d788b>] __vfs_write+0xeb/0x2a0 fs/read_write.c:489
> [<ffffffff812d8a63>] vfs_write+0x113/0x290 fs/read_write.c:538
> [< inline >] SYSC_write fs/read_write.c:585
> [<ffffffff812da27b>] SyS_write+0xbb/0x170 fs/read_write.c:577
> [<ffffffff82175fd1>] entry_SYSCALL_64_fastpath+0x31/0x9a
> arch/x86/entry/entry_64.S:187
>
> -> #0 (&tty->atomic_write_lock){+.+.+.}:
> [< inline >] __mutex_lock_common kernel/locking/mutex.c:518
> [<ffffffff82170525>] mutex_lock_interruptible_nested+0xa5/0x660
> kernel/locking/mutex.c:647
> [<ffffffff81774876>] tty_write_lock+0x46/0x70 drivers/tty/tty_io.c:1093
> [<ffffffff8177a5a4>] tty_send_xchar+0x94/0x130
> drivers/tty/tty_io.c:1289
> [<ffffffff81786507>] n_tty_ioctl_helper+0x1a7/0x210
> drivers/tty/tty_ioctl.c:1158
> [<ffffffff8177f6e9>] n_tty_ioctl+0xe9/0x1e0 drivers/tty/n_tty.c:2514
> [<ffffffff8177979c>] tty_ioctl+0xa4c/0x1650 drivers/tty/tty_io.c:2945
> [< inline >] vfs_ioctl fs/ioctl.c:43
> [<ffffffff812fdf0f>] do_vfs_ioctl+0x53f/0x980 fs/ioctl.c:607
> [< inline >] SYSC_ioctl fs/ioctl.c:622
> [<ffffffff812fe3df>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:613
> [<ffffffff82175fd1>] entry_SYSCALL_64_fastpath+0x31/0x9a
> arch/x86/entry/entry_64.S:187
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&tty->termios_rwsem);
> lock(&tty->atomic_write_lock);
> lock(&tty->termios_rwsem);
> lock(&tty->atomic_write_lock);
>
> *** DEADLOCK ***
Thanks for the report, Dmitry.
Please re-test with the accompanying patch.
Regards,
Peter Hurley
--- >% ---
Subject: [PATCH] tty: Fix tty_send_xchar() lock order inversion
The correct lock order is atomic_write_lock => termios_rwsem, as
established by tty_write() => n_tty_write().
Fixes: c274f6ef1c666 ("tty: Hold termios_rwsem for tcflow(TCIxxx)")
Reported-by: Dmitry Vyukov <[email protected]>
Cc: <[email protected]> # v3.18+
Signed-off-by: Peter Hurley <[email protected]>
---
drivers/tty/tty_io.c | 4 ++++
drivers/tty/tty_ioctl.c | 4 ----
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 2f8c21e..346a1a5 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1283,18 +1283,22 @@ int tty_send_xchar(struct tty_struct *tty, char ch)
int was_stopped = tty->stopped;
if (tty->ops->send_xchar) {
+ down_read(&tty->termios_rwsem);
tty->ops->send_xchar(tty, ch);
+ up_read(&tty->termios_rwsem);
return 0;
}
if (tty_write_lock(tty, 0) < 0)
return -ERESTARTSYS;
+ down_read(&tty->termios_rwsem);
if (was_stopped)
start_tty(tty);
tty->ops->write(tty, &ch, 1);
if (was_stopped)
stop_tty(tty);
+ up_read(&tty->termios_rwsem);
tty_write_unlock(tty);
return 0;
}
diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index b8c5c12..0ea3513 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -1140,16 +1140,12 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct
file *file,
spin_unlock_irq(&tty->flow_lock);
break;
case TCIOFF:
- down_read(&tty->termios_rwsem);
if (STOP_CHAR(tty) != __DISABLED_CHAR)
retval = tty_send_xchar(tty, STOP_CHAR(tty));
- up_read(&tty->termios_rwsem);
break;
case TCION:
- down_read(&tty->termios_rwsem);
if (START_CHAR(tty) != __DISABLED_CHAR)
retval = tty_send_xchar(tty, START_CHAR(tty));
- up_read(&tty->termios_rwsem);
break;
default:
return -EINVAL;
--
2.6.3
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
