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authorPeter Hurley <peter@hurleysoftware.com>2013-03-11 16:44:45 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-03-18 16:52:24 -0700
commite7f3880cd9b98c5bf9391ae7acdec82b75403776 (patch)
treecb8a2d9cff9d756ea7d0947ad58318a65b218ee0 /drivers/net/ppp/ppp_synctty.c
parenttty: Remove redundant tty_wait_until_sent() (diff)
downloadlinux-dev-e7f3880cd9b98c5bf9391ae7acdec82b75403776.tar.xz
linux-dev-e7f3880cd9b98c5bf9391ae7acdec82b75403776.zip
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.c2
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: