Currently there is a lock order problem between the console lock and the kernfs s_active lock of the console driver's bind sysfs entry. When writing to the sysfs entry the lock order is first s_active then console lock, when unregistering the console driver via do_unregister_con_driver() the order is the opposite. See the below bugzilla reference for one instance of a lockdep backtrace.
Fix this by unregistering the console driver from a deferred work, where we can safely drop the console lock while unregistering the device and corresponding sysfs entries (which in turn acquire s_active). Note that we have to keep the console driver slot in the registered_con_driver array reserved for the driver that's being unregistered until it's fully removed. Otherwise a concurrent call to do_register_con_driver could try to reuse the same slot and fail when registering the corresponding device with a minor index that's still in use. Reference: https://bugs.freedesktop.org/show_bug.cgi?id=70523 Signed-off-by: Imre Deak <imre.d...@intel.com> --- drivers/tty/vt/vt.c | 51 +++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 41 insertions(+), 10 deletions(-) diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index 5dd1880..b9edc77 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -108,6 +108,7 @@ #define CON_DRIVER_FLAG_MODULE 1 #define CON_DRIVER_FLAG_INIT 2 #define CON_DRIVER_FLAG_ATTR 4 +#define CON_DRIVER_FLAG_ZOMBIE 8 struct con_driver { const struct consw *con; @@ -153,6 +154,7 @@ static int set_vesa_blanking(char __user *p); static void set_cursor(struct vc_data *vc); static void hide_cursor(struct vc_data *vc); static void console_callback(struct work_struct *ignored); +static void con_driver_unregister_callback(struct work_struct *ignored); static void blank_screen_t(unsigned long dummy); static void set_palette(struct vc_data *vc); @@ -180,6 +182,7 @@ static int blankinterval = 10*60; core_param(consoleblank, blankinterval, int, 0444); static DECLARE_WORK(console_work, console_callback); +static DECLARE_WORK(con_driver_unregister_work, con_driver_unregister_callback); /* * fg_console is the current virtual console, @@ -3597,7 +3600,8 @@ static int do_register_con_driver(const struct consw *csw, int first, int last) for (i = 0; i < MAX_NR_CON_DRIVER; i++) { con_driver = ®istered_con_driver[i]; - if (con_driver->con == NULL) { + if (con_driver->con == NULL && + !(con_driver->flag & CON_DRIVER_FLAG_ZOMBIE)) { con_driver->con = csw; con_driver->desc = desc; con_driver->node = i; @@ -3660,16 +3664,10 @@ int do_unregister_con_driver(const struct consw *csw) if (con_driver->con == csw && con_driver->flag & CON_DRIVER_FLAG_MODULE) { - vtconsole_deinit_device(con_driver); - device_destroy(vtconsole_class, - MKDEV(0, con_driver->node)); con_driver->con = NULL; - con_driver->desc = NULL; - con_driver->dev = NULL; - con_driver->node = 0; - con_driver->flag = 0; - con_driver->first = 0; - con_driver->last = 0; + con_driver->flag = CON_DRIVER_FLAG_ZOMBIE; + schedule_work(&con_driver_unregister_work); + return 0; } } @@ -3678,6 +3676,39 @@ int do_unregister_con_driver(const struct consw *csw) } EXPORT_SYMBOL_GPL(do_unregister_con_driver); +static void con_driver_unregister_callback(struct work_struct *ignored) +{ + int i; + + console_lock(); + + for (i = 0; i < MAX_NR_CON_DRIVER; i++) { + struct con_driver *con_driver = ®istered_con_driver[i]; + + if (!(con_driver->flag & CON_DRIVER_FLAG_ZOMBIE)) + continue; + + console_unlock(); + + vtconsole_deinit_device(con_driver); + device_destroy(vtconsole_class, MKDEV(0, con_driver->node)); + + if (WARN_ON_ONCE(con_driver->con)) + con_driver->con = NULL; + con_driver->desc = NULL; + con_driver->dev = NULL; + con_driver->node = 0; + WARN_ON_ONCE(con_driver->flag != CON_DRIVER_FLAG_ZOMBIE); + con_driver->flag = 0; + con_driver->first = 0; + con_driver->last = 0; + + console_lock(); + } + + console_unlock(); +} + /* * If we support more console drivers, this function is used * when a driver wants to take over some existing consoles -- 1.8.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
