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authorPeter Hurley <peter@hurleysoftware.com>2013-03-12 00:44:45 +0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-03-19 03:52:24 +0400
commite7f3880cd9b98c5bf9391ae7acdec82b75403776 (patch)
treecb8a2d9cff9d756ea7d0947ad58318a65b218ee0 /drivers/tty/tty_ioctl.c
parentbe3971166d93a401105952672dab2eac6542cb57 (diff)
downloadlinux-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.c28
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);