From 3d954c5c7239c6478b78450a03b4a53e1f93b158 Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 15 Jul 2021 21:39:57 +0206 Subject: [PATCH] printk: remove NMI tracking All NMI contexts are handled the same as the safe context: store the message and defer printing. There is no need to have special NMI context tracking for this. Using in_nmi() is enough. There are several parts of the kernel that are manually calling into the printk NMI context tracking in order to cause general printk deferred printing: arch/arm/kernel/smp.c arch/powerpc/kexec/crash.c kernel/trace/trace.c For arm/kernel/smp.c and powerpc/kexec/crash.c, provide a new function pair printk_deferred_enter/exit that explicitly achieves the same objective. For ftrace, remove the printk context manipulation completely. It was added in commit 6303a569c680 ("printk/nmi: Prevent deadlock when accessing the main log buffer in NMI"). The purpose was to enforce storing messages directly into the ring buffer even in NMI context. It really should have only modified the behavior in NMI context. There is no need for a special behavior any longer. All messages are always stored directly now. The console deferring is handled transparently in vprintk(). Signed-off-by: John Ogness [pmladek@suse.com: Remove special handling in ftrace.c completely. Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-5-john.ogness@linutronix.de --- arch/arm/kernel/smp.c | 4 ++-- arch/powerpc/kexec/crash.c | 2 +- include/linux/hardirq.h | 2 -- include/linux/printk.h | 31 +++++++++++++++++++------------ init/Kconfig | 5 ----- kernel/printk/internal.h | 8 -------- kernel/printk/printk_safe.c | 37 +------------------------------------ kernel/trace/trace.c | 2 -- 8 files changed, 23 insertions(+), 68 deletions(-) diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index c7bb168b0d97c..842427ff2b3cb 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -667,9 +667,9 @@ static void do_handle_IPI(int ipinr) break; case IPI_CPU_BACKTRACE: - printk_nmi_enter(); + printk_deferred_enter(); nmi_cpu_backtrace(get_irq_regs()); - printk_nmi_exit(); + printk_deferred_exit(); break; default: diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c index 0196d0c211aca..1070378c8e353 100644 --- a/arch/powerpc/kexec/crash.c +++ b/arch/powerpc/kexec/crash.c @@ -313,7 +313,7 @@ void default_machine_crash_shutdown(struct pt_regs *regs) int (*old_handler)(struct pt_regs *regs); /* Avoid hardlocking with irresponsive CPU holding logbuf_lock */ - printk_nmi_enter(); + printk_deferred_enter(); /* * This function is only called after the system diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index 69bc86ea382c2..76878b357ffa9 100644 --- a/include/linux/hardirq.h +++ b/include/linux/hardirq.h @@ -116,7 +116,6 @@ extern void rcu_nmi_exit(void); do { \ lockdep_off(); \ arch_nmi_enter(); \ - printk_nmi_enter(); \ BUG_ON(in_nmi() == NMI_MASK); \ __preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \ } while (0) @@ -135,7 +134,6 @@ extern void rcu_nmi_exit(void); do { \ BUG_ON(!in_nmi()); \ __preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \ - printk_nmi_exit(); \ arch_nmi_exit(); \ lockdep_on(); \ } while (0) diff --git a/include/linux/printk.h b/include/linux/printk.h index 719d919f9b673..a1379df432518 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -149,18 +149,6 @@ static inline __printf(1, 2) __cold void early_printk(const char *s, ...) { } #endif -#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 */ - struct dev_printk_info; #ifdef CONFIG_PRINTK @@ -180,6 +168,16 @@ int printk(const char *fmt, ...); */ __printf(1, 2) __cold int printk_deferred(const char *fmt, ...); +extern void __printk_safe_enter(void); +extern void __printk_safe_exit(void); +/* + * The printk_deferred_enter/exit macros are available only as a hack for + * some code paths that need to defer all printk console printing. Interrupts + * must be disabled for the deferred duration. + */ +#define printk_deferred_enter __printk_safe_enter +#define printk_deferred_exit __printk_safe_exit + /* * Please don't use printk_ratelimit(), because it shares ratelimiting state * with all other unrelated printk_ratelimit() callsites. Instead use @@ -224,6 +222,15 @@ int printk_deferred(const char *s, ...) { return 0; } + +static inline void printk_deferred_enter(void) +{ +} + +static inline void printk_deferred_exit(void) +{ +} + static inline int printk_ratelimit(void) { return 0; diff --git a/init/Kconfig b/init/Kconfig index a61c92066c2e4..9c0510693543f 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1506,11 +1506,6 @@ config PRINTK very difficult to diagnose system problems, saying N here is strongly discouraged. -config PRINTK_NMI - def_bool y - depends on PRINTK - depends on HAVE_NMI - config BUG bool "BUG() support" if EXPERT default y diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 6cc35c5de8906..b6d310c72fc97 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -6,12 +6,6 @@ #ifdef CONFIG_PRINTK -#define PRINTK_SAFE_CONTEXT_MASK 0x007ffffff -#define PRINTK_NMI_DIRECT_CONTEXT_MASK 0x008000000 -#define PRINTK_NMI_CONTEXT_MASK 0xff0000000 - -#define PRINTK_NMI_CONTEXT_OFFSET 0x010000000 - __printf(4, 0) int vprintk_store(int facility, int level, const struct dev_printk_info *dev_info, @@ -19,8 +13,6 @@ int vprintk_store(int facility, int level, __printf(1, 0) int vprintk_default(const char *fmt, va_list args); __printf(1, 0) int vprintk_deferred(const char *fmt, va_list args); -void __printk_safe_enter(void); -void __printk_safe_exit(void); bool printk_percpu_data_ready(void); diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index 29c580dac93dd..ef0f9a2044da1 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -4,12 +4,9 @@ */ #include -#include -#include #include #include #include -#include #include #include @@ -17,35 +14,6 @@ static DEFINE_PER_CPU(int, printk_context); -#ifdef CONFIG_PRINTK_NMI -void noinstr printk_nmi_enter(void) -{ - this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET); -} - -void noinstr printk_nmi_exit(void) -{ - this_cpu_sub(printk_context, PRINTK_NMI_CONTEXT_OFFSET); -} - -/* - * Marks a code that might produce many messages in NMI context - * and the risk of losing them is more critical than eventual - * reordering. - */ -void printk_nmi_direct_enter(void) -{ - if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK) - this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK); -} - -void printk_nmi_direct_exit(void) -{ - this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK); -} - -#endif /* CONFIG_PRINTK_NMI */ - /* Can be preempted by NMI. */ void __printk_safe_enter(void) { @@ -70,10 +38,7 @@ asmlinkage int vprintk(const char *fmt, va_list args) * Use the main logbuf even in NMI. But avoid calling console * drivers that might have their own locks. */ - if (this_cpu_read(printk_context) & - (PRINTK_NMI_DIRECT_CONTEXT_MASK | - PRINTK_NMI_CONTEXT_MASK | - PRINTK_SAFE_CONTEXT_MASK)) { + if (this_cpu_read(printk_context) || in_nmi()) { int len; len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args); diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index d23a09d3eb37b..2f41311c61d72 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -9647,7 +9647,6 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) tracing_off(); local_irq_save(flags); - printk_nmi_direct_enter(); /* Simulate the iterator */ trace_init_global_iter(&iter); @@ -9729,7 +9728,6 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) atomic_dec(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled); } atomic_dec(&dump_running); - printk_nmi_direct_exit(); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(ftrace_dump); -- 2.39.5