On Fri 2019-04-26 14:33:01, Sergey Senozhatsky wrote: > We need to take console_sem lock when we iterate console drivers > list. Otherwise, another CPU can concurrently modify console drivers > list or console drivers. Current register_console() has several > race conditions - for_each_console() must be done under console_sem. > > Factor out console registration code and hold console_sem throughout > entire registration process. Note that we need to unlock console_sem > and lock it again after we added new console to the list and before > we unregister boot consoles. This might look a bit weird, but this > is how we print pending logbuf messages to all registered and > available consoles.
My main concern was whether we could call newcon->setup() under console_lock. I checked many console drivers and all looked safe. There should not be much reasons to do it. > Signed-off-by: Sergey Senozhatsky <[email protected]> > --- > kernel/printk/printk.c | 15 ++++++++++----- > 1 file changed, 10 insertions(+), 5 deletions(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 3ac71701afa3..3b36e26d4a51 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -2771,7 +2771,6 @@ void register_console(struct console *newcon) > * Put this console in the list - keep the > * preferred driver at the head of the list. > */ > - console_lock(); > if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) { > newcon->next = console_drivers; > console_drivers = newcon; > @@ -2818,6 +2817,7 @@ void register_console(struct console *newcon) > > console_unlock(); > console_sysfs_notify(); > + console_lock(); I have got an idea how to get rid of this weirdness: 1. The check for bcon seems to be just an optimization. There is not need to remove boot consoles when there are none. 2. The condition (newcon->flags & (CON_CONSDEV|CON_BOOT)) == CON_CONSDEV) is valid only when the preferred console was really added. Therefore we could move the code to a separate function, e.g. void unregister_boot_consoles(void) { struct console *bcon; console_lock(); for_each_console(bcon) if (bcon->flags & CON_BOOT) __unregister_console(bcon); } console_unlock(); console_sysfs_notify(); } Then we could do something like: void register_console(struct console *newcon) { bool newcon_is_preferred = false; console_lock(); __register_console(newcon); if ((newcon->flags & (CON_CONSDEV|CON_BOOT)) == CON_CONSDEV) newcon_is_preferred = true; console_unlock(); console_sysfs_notify(); /* * By unregistering the bootconsoles after we enable the real console * we get the "console xxx enabled" message on all the consoles - * boot consoles, real consoles, etc - this is to ensure that end * users know there might be something in the kernel's log buffer that * went to the bootconsole (that they do not see on the real console) */ if (newcon_is_preferred && !keep_bootcon) unregister_boot_consoles(); } How does that sound? Otherwise, the patch looks fine to me. Best Regards, Petr
