The following pattern in register_console() is not completely safe: for_each_console(bcon) if (bcon->flags & CON_BOOT) unregister_console(bcon);
Because, in theory, console drivers list and console drivers can be modified concurrently from another CPU. We need to grab console_sem lock, which protects console drivers list and console drivers, before we start iterating console drivers list. Factor out __unregister_console(), which will be called from unregister_console() and register_console(), in both cases under console_sem lock. Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com> --- kernel/printk/printk.c | 98 ++++++++++++++++++++++++------------------ 1 file changed, 56 insertions(+), 42 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 17102fd4c136..b0e361ca1bea 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2605,6 +2605,48 @@ static int __init keep_bootcon_setup(char *str) early_param("keep_bootcon", keep_bootcon_setup); +static int __unregister_console(struct console *console) +{ + struct console *a, *b; + int res; + + pr_info("%sconsole [%s%d] disabled\n", + (console->flags & CON_BOOT) ? "boot" : "", + console->name, console->index); + + res = _braille_unregister_console(console); + if (res) + return res; + + res = 1; + if (console_drivers == console) { + console_drivers = console->next; + res = 0; + } else if (console_drivers) { + for (a = console_drivers->next, b = console_drivers; + a; b = a, a = b->next) { + if (a == console) { + b->next = a->next; + res = 0; + break; + } + } + } + + if (!res && (console->flags & CON_EXTENDED)) + nr_ext_console_drivers--; + + /* + * If this isn't the last console and it has CON_CONSDEV set, we + * need to set it on the next preferred console. + */ + if (console_drivers != NULL && console->flags & CON_CONSDEV) + console_drivers->flags |= CON_CONSDEV; + + console->flags &= ~CON_ENABLED; + return res; +} + /* * The console driver calls this routine during kernel initialization * to register the console printing procedure with printk() and to @@ -2777,62 +2819,34 @@ void register_console(struct console *newcon) pr_info("%sconsole [%s%d] enabled\n", (newcon->flags & CON_BOOT) ? "boot" : "" , newcon->name, newcon->index); - if (bcon && - ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) && - !keep_bootcon) { - /* We need to iterate through all boot consoles, to make + + if (keep_bootcon) + return; + + if (bcon && (newcon->flags & (CON_CONSDEV|CON_BOOT)) == CON_CONSDEV) { + console_lock(); + /* + * We need to iterate through all boot consoles, to make * sure we print everything out, before we unregister them. */ for_each_console(bcon) if (bcon->flags & CON_BOOT) - unregister_console(bcon); + __unregister_console(bcon); + console_unlock(); + console_sysfs_notify(); } } EXPORT_SYMBOL(register_console); int unregister_console(struct console *console) { - struct console *a, *b; - int res; - - pr_info("%sconsole [%s%d] disabled\n", - (console->flags & CON_BOOT) ? "boot" : "" , - console->name, console->index); - - res = _braille_unregister_console(console); - if (res) - return res; + int ret; - res = 1; console_lock(); - if (console_drivers == console) { - console_drivers=console->next; - res = 0; - } else if (console_drivers) { - for (a=console_drivers->next, b=console_drivers ; - a; b=a, a=b->next) { - if (a == console) { - b->next = a->next; - res = 0; - break; - } - } - } - - if (!res && (console->flags & CON_EXTENDED)) - nr_ext_console_drivers--; - - /* - * If this isn't the last console and it has CON_CONSDEV set, we - * need to set it on the next preferred console. - */ - if (console_drivers != NULL && console->flags & CON_CONSDEV) - console_drivers->flags |= CON_CONSDEV; - - console->flags &= ~CON_ENABLED; + ret = __unregister_console(console); console_unlock(); console_sysfs_notify(); - return res; + return ret; } EXPORT_SYMBOL(unregister_console); -- 2.21.0