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| author | Peter Hurley <peter@hurleysoftware.com> | 2013-03-12 00:44:45 +0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-03-19 03:52:24 +0400 |
| commit | e7f3880cd9b98c5bf9391ae7acdec82b75403776 (patch) | |
| tree | cb8a2d9cff9d756ea7d0947ad58318a65b218ee0 /drivers/tty/tty_ioctl.c | |
| parent | be3971166d93a401105952672dab2eac6542cb57 (diff) | |
| download | linux-e7f3880cd9b98c5bf9391ae7acdec82b75403776.tar.xz | |
tty: Fix recursive deadlock in tty_perform_flush()
tty_perform_flush() can deadlock when called while holding
a line discipline reference. By definition, all ldisc drivers
hold a ldisc reference, so calls originating from ldisc drivers
must not block for a ldisc reference.
The deadlock can occur when:
CPU 0 | CPU 1
|
tty_ldisc_ref(tty) |
.... | <line discipline halted>
tty_ldisc_ref_wait(tty) |
|
CPU 0 cannot progess because it cannot obtain an ldisc reference
with the line discipline has been halted (thus no new references
are granted).
CPU 1 cannot progress because an outstanding ldisc reference
has not been released.
An in-tree call-tree audit of tty_perform_flush() [1] shows 5
ldisc drivers calling tty_perform_flush() indirectly via
n_tty_ioctl_helper() and 2 ldisc drivers calling directly.
A single tty driver safely uses the function.
[1]
Recursive usage:
/* These functions are line discipline ioctls and thus
* recursive wrt line discipline references */
tty_perform_flush() - ./drivers/tty/tty_ioctl.c
n_tty_ioctl_helper()
hci_uart_tty_ioctl(default) - drivers/bluetooth/hci_ldisc.c (N_HCI)
n_hdlc_tty_ioctl(default) - drivers/tty/n_hdlc.c (N_HDLC)
gsmld_ioctl(default) - drivers/tty/n_gsm.c (N_GSM0710)
n_tty_ioctl(default) - drivers/tty/n_tty.c (N_TTY)
gigaset_tty_ioctl(default) - drivers/isdn/gigaset/ser-gigaset.c (N_GIGASET_M101)
ppp_synctty_ioctl(TCFLSH) - drivers/net/ppp/pps_synctty.c
ppp_asynctty_ioctl(TCFLSH) - drivers/net/ppp/ppp_async.c
Non-recursive use:
tty_perform_flush() - drivers/tty/tty_ioctl.c
ipw_ioctl(TCFLSH) - drivers/tty/ipwireless/tty.c
/* This function is a tty i/o ioctl method, which
* is invoked by tty_ioctl() */
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/tty_ioctl.c')
| -rw-r--r-- | drivers/tty/tty_ioctl.c | 28 |
1 files changed, 19 insertions, 9 deletions
diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c index 28715e48b2f7..d119034877de 100644 --- a/drivers/tty/tty_ioctl.c +++ b/drivers/tty/tty_ioctl.c @@ -1122,14 +1122,12 @@ int tty_mode_ioctl(struct tty_struct *tty, struct file *file, } EXPORT_SYMBOL_GPL(tty_mode_ioctl); -int tty_perform_flush(struct tty_struct *tty, unsigned long arg) + +/* Caller guarantees ldisc reference is held */ +static int __tty_perform_flush(struct tty_struct *tty, unsigned long arg) { - struct tty_ldisc *ld; - int retval = tty_check_change(tty); - if (retval) - return retval; + struct tty_ldisc *ld = tty->ldisc; - ld = tty_ldisc_ref_wait(tty); switch (arg) { case TCIFLUSH: if (ld && ld->ops->flush_buffer) { @@ -1147,12 +1145,24 @@ int tty_perform_flush(struct tty_struct *tty, unsigned long arg) tty_driver_flush_buffer(tty); break; default: - tty_ldisc_deref(ld); return -EINVAL; } - tty_ldisc_deref(ld); return 0; } + +int tty_perform_flush(struct tty_struct *tty, unsigned long arg) +{ + struct tty_ldisc *ld; + int retval = tty_check_change(tty); + if (retval) + return retval; + + ld = tty_ldisc_ref_wait(tty); + retval = __tty_perform_flush(tty, arg); + if (ld) + tty_ldisc_deref(ld); + return retval; +} EXPORT_SYMBOL_GPL(tty_perform_flush); int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file, @@ -1191,7 +1201,7 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file, } return 0; case TCFLSH: - return tty_perform_flush(tty, arg); + return __tty_perform_flush(tty, arg); default: /* Try the mode commands */ return tty_mode_ioctl(tty, file, cmd, arg); |