On Wed, Nov 11, 2015 at 1:05 PM, Peter Hurley <[email protected]> wrote: > 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.
The patch fixes the deadlock. Thanks for the quick fix! Tested-by: Dmitry Vyukov <[email protected]> > 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/
