Hi Imre, On 12/12/2014 11:38 AM, Imre Deak wrote: > 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.
This description didn't make sense to me because the driver core doesn't try to take the console_lock. So I had to go pull the lockdep report and I'm not sure I agree with your analysis. I see a three-way dependency which includes the fb atomic notifier call chain? Regards, Peter Hurley > 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 > -- 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/
