From 22eceb8bf3e8f1f9b2f566062d06b25807725d7f Mon Sep 17 00:00:00 2001 From: Hans de Goede Date: Tue, 19 Jun 2018 13:57:26 +0200 Subject: printk: Make CONSOLE_LOGLEVEL_QUIET configurable The goal of passing the "quiet" option to the kernel is for the kernel to be quiet unless something really is wrong. Sofar passing quiet has been (mostly) equivalent to passing loglevel=4 on the kernel commandline. Which means to show any messages with a level of KERN_ERR or higher severity on the console. In practice this often does not result in a quiet boot though, since there are many false-positive or otherwise harmless error messages printed, defeating the purpose of the quiet option. Esp. the ACPICA code is really bad wrt this, but there are plenty of others too. This commit makes CONSOLE_LOGLEVEL_QUIET configurable. This for example will allow distros which want quiet to really mean quiet to set CONSOLE_LOGLEVEL_QUIET so that only messages with a higher severity then KERN_ERR (CRIT, ALERT, EMERG) get printed, avoiding an endless game of whack-a-mole silencing harmless error messages. Link: http://lkml.kernel.org/r/20180619115726.3098-1-hdegoede@redhat.com To: Petr Mladek To: Sergey Senozhatsky Cc: Hans de Goede Cc: Steven Rostedt Cc: linux-kernel@vger.kernel.org Signed-off-by: Hans de Goede Acked-by: Steven Rostedt (VMware) Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek --- include/linux/printk.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'include/linux') diff --git a/include/linux/printk.h b/include/linux/printk.h index 6d7e800affd8..18602bb3eca8 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -50,15 +50,15 @@ static inline const char *printk_skip_headers(const char *buffer) /* We show everything that is MORE important than this.. */ #define CONSOLE_LOGLEVEL_SILENT 0 /* Mum's the word */ #define CONSOLE_LOGLEVEL_MIN 1 /* Minimum loglevel we let people use */ -#define CONSOLE_LOGLEVEL_QUIET 4 /* Shhh ..., when booted with "quiet" */ #define CONSOLE_LOGLEVEL_DEBUG 10 /* issue debug messages */ #define CONSOLE_LOGLEVEL_MOTORMOUTH 15 /* You can't shut this one up */ /* - * Default used to be hard-coded at 7, we're now allowing it to be set from - * kernel config. + * Default used to be hard-coded at 7, quiet used to be hardcoded at 4, + * we're now allowing both to be set from kernel config. */ #define CONSOLE_LOGLEVEL_DEFAULT CONFIG_CONSOLE_LOGLEVEL_DEFAULT +#define CONSOLE_LOGLEVEL_QUIET CONFIG_CONSOLE_LOGLEVEL_QUIET extern int console_printk[]; -- cgit v1.2.3 From 03fc7f9c99c1e7ae2925d459e8487f1a6f199f79 Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Wed, 27 Jun 2018 16:20:28 +0200 Subject: printk/nmi: Prevent deadlock when accessing the main log buffer in NMI The commit 719f6a7040f1bdaf96 ("printk: Use the main logbuf in NMI when logbuf_lock is available") brought back the possible deadlocks in printk() and NMI. The check of logbuf_lock is done only in printk_nmi_enter() to prevent mixed output. But another CPU might take the lock later, enter NMI, and: + Both NMIs might be serialized by yet another lock, for example, the one in nmi_cpu_backtrace(). + The other CPU might get stopped in NMI, see smp_send_stop() in panic(). The only safe solution is to use trylock when storing the message into the main log-buffer. It might cause reordering when some lines go to the main lock buffer directly and others are delayed via the per-CPU buffer. It means that it is not useful in general. This patch replaces the problematic NMI deferred context with NMI direct context. It can be used to mark a code that might produce many messages in NMI and the risk of losing them is more critical than problems with eventual reordering. The context is then used when dumping trace buffers on oops. It was the primary motivation for the original fix. Also the reordering is even smaller issue there because some traces have their own time stamps. Finally, nmi_cpu_backtrace() need not longer be serialized because it will always us the per-CPU buffers again. Fixes: 719f6a7040f1bdaf96 ("printk: Use the main logbuf in NMI when logbuf_lock is available") Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20180627142028.11259-1-pmladek@suse.com To: Steven Rostedt Cc: Peter Zijlstra Cc: Tetsuo Handa Cc: Sergey Senozhatsky Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek --- include/linux/printk.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux') diff --git a/include/linux/printk.h b/include/linux/printk.h index 6d7e800affd8..3ede9f46a494 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -148,9 +148,13 @@ void early_printk(const char *s, ...) { } #ifdef CONFIG_PRINTK_NMI extern void printk_nmi_enter(void); extern void printk_nmi_exit(void); +extern void printk_nmi_direct_enter(void); +extern void printk_nmi_direct_exit(void); #else static inline void printk_nmi_enter(void) { } static inline void printk_nmi_exit(void) { } +static inline void printk_nmi_direct_enter(void) { } +static inline void printk_nmi_direct_exit(void) { } #endif /* PRINTK_NMI */ #ifdef CONFIG_PRINTK -- cgit v1.2.3