Messages in this thread Patch in this message | | | From | Sergey Senozhatsky <> | Subject | [PATCHv2 3/4] printk: factor out register_console() code | Date | Fri, 26 Apr 2019 14:33:01 +0900 |
| |
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.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> --- 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 @@ -2666,7 +2666,7 @@ static int __unregister_console(struct console *console) * - Once a "real" console is registered, any attempt to register a * bootconsoles will be rejected */ -void register_console(struct console *newcon) +static void __register_console(struct console *newcon) { int i; unsigned long flags; @@ -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(); if (keep_bootcon) return; @@ -2830,14 +2830,19 @@ void register_console(struct console *newcon) * went to the bootconsole (that they do not see on the real console) */ if (bcon && (newcon->flags & (CON_CONSDEV|CON_BOOT)) == CON_CONSDEV) { - console_lock(); for_each_console(bcon) if (bcon->flags & CON_BOOT) __unregister_console(bcon); - console_unlock(); - console_sysfs_notify(); } } + +void register_console(struct console *newcon) +{ + console_lock(); + __register_console(newcon); + console_unlock(); + console_sysfs_notify(); +} EXPORT_SYMBOL(register_console); int unregister_console(struct console *console) -- 2.21.0
| |