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| author | Peter Hurley <peter@hurleysoftware.com> | 2013-03-11 16:44:45 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-03-18 16:52:24 -0700 |
| commit | e7f3880cd9b98c5bf9391ae7acdec82b75403776 (patch) | |
| tree | cb8a2d9cff9d756ea7d0947ad58318a65b218ee0 /drivers/net/ppp/ppp_synctty.c | |
| parent | be3971166d93a401105952672dab2eac6542cb57 (diff) | |
| download | linux-e7f3880cd9b98c5bf9391ae7acdec82b75403776.tar.bz2 | |
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/net/ppp/ppp_synctty.c')
| -rw-r--r-- | drivers/net/ppp/ppp_synctty.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/net/ppp/ppp_synctty.c b/drivers/net/ppp/ppp_synctty.c index 1a12033d2efa..bdf3b13a71a8 100644 --- a/drivers/net/ppp/ppp_synctty.c +++ b/drivers/net/ppp/ppp_synctty.c @@ -355,7 +355,7 @@ ppp_synctty_ioctl(struct tty_struct *tty, struct file *file, /* flush our buffers and the serial port's buffer */ if (arg == TCIOFLUSH || arg == TCOFLUSH) ppp_sync_flush_output(ap); - err = tty_perform_flush(tty, arg); + err = n_tty_ioctl_helper(tty, file, cmd, arg); break; case FIONREAD: |