Messages in this thread | | | Date | Mon, 21 Nov 2022 14:36:14 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH printk v6 11/40] printk: introduce console_list_lock |
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On Mon 2022-11-21 12:16:12, John Ogness wrote: > Currently there exist races in register_console(), where the types > of registered consoles are checked (without holding the console_lock) > and then after acquiring the console_lock, it is assumed that the list > has not changed. Also, some code that performs console_unregister() > make similar assumptions. > > It might be possible to fix these races using the console_lock. But > it would require a complex analysis of all console drivers to make > sure that the console_lock is not taken in match() and setup() > callbacks. And we really prefer to split up and reduce the > responsibilities of console_lock rather than expand its complexity. > Therefore, introduce a new console_list_lock to provide full > synchronization for any console list changes. > > In addition, also use console_list_lock for synchronization of > console->flags updates. All flags are either static or modified only > during the console registration. There are only two exceptions. > > The first exception is CON_ENABLED, which is also modified by > console_start()/console_stop(). Therefore, these functions must > also take the console_list_lock. > > The second exception is when the flags are modified by the console > driver init code before the console is registered. These will be > ignored because they are not visible to the rest of the system > via the console_drivers list. > > Note that one of the various responsibilities of the console_lock is > also intended to provide console list and console->flags > synchronization. Later changes will update call sites relying on the > console_lock for these purposes. Once all call sites have been > updated, the console_lock will be relieved of synchronizing > console_list and console->flags updates. > > Suggested-by: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: John Ogness <john.ogness@linutronix.de> > Reviewed-by: Petr Mladek <pmladek@suse.com> > --- > Stephen reported [0] a build failure with linux-next. The problem was a > missing EXPORT of @lockdep_assert_console_list_lock_held for when > drivers are built as modules. > > [0] https://lore.kernel.org/lkml/20221121110041.1d2c635b@canb.auug.org.au
JFYI, the branch rework/console-list-lock in printk/linux.git has been rebased using this version of the patch.
Thanks a lot for the fix.
Best Regards, Petr
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