From 766c268bc6d39b8124e50d075a36b8a3305bc8e2 Mon Sep 17 00:00:00 2001 From: John Ogness Date: Thu, 17 Jun 2021 11:56:50 +0206 Subject: lib/dump_stack: move cpu lock to printk.c dump_stack() implements its own cpu-reentrant spinning lock to best-effort serialize stack traces in the printk log. However, there are other functions (such as show_regs()) that can also benefit from this serialization. Move the cpu-reentrant spinning lock (cpu lock) into new helper functions printk_cpu_lock_irqsave()/printk_cpu_unlock_irqrestore() so that it is available for others as well. For !CONFIG_SMP the cpu lock is a NOP. Note that having multiple cpu locks in the system can easily lead to deadlock. Code needing a cpu lock should use the printk cpu lock, since the printk cpu lock could be acquired from any code and any context. Also note that it is not necessary for a cpu lock to disable interrupts. However, in upcoming work this cpu lock will be used for emergency tasks (for example, atomic consoles during kernel crashes) and any interruptions while holding the cpu lock should be avoided if possible. Signed-off-by: John Ogness Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek [pmladek@suse.com: Backported on top of 5.13-rc1.] Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210617095051.4808-2-john.ogness@linutronix.de --- lib/dump_stack.c | 38 ++------------------------------------ 1 file changed, 2 insertions(+), 36 deletions(-) (limited to 'lib/dump_stack.c') diff --git a/lib/dump_stack.c b/lib/dump_stack.c index f5a33b6f773f..5ebf4375fa8c 100644 --- a/lib/dump_stack.c +++ b/lib/dump_stack.c @@ -84,50 +84,16 @@ static void __dump_stack(void) * * Architectures can override this implementation by implementing its own. */ -#ifdef CONFIG_SMP -static atomic_t dump_lock = ATOMIC_INIT(-1); - asmlinkage __visible void dump_stack(void) { unsigned long flags; - int was_locked; - int old; - int cpu; /* * Permit this cpu to perform nested stack dumps while serialising * against other CPUs */ -retry: - local_irq_save(flags); - cpu = smp_processor_id(); - old = atomic_cmpxchg(&dump_lock, -1, cpu); - if (old == -1) { - was_locked = 0; - } else if (old == cpu) { - was_locked = 1; - } else { - local_irq_restore(flags); - /* - * Wait for the lock to release before jumping to - * atomic_cmpxchg() in order to mitigate the thundering herd - * problem. - */ - do { cpu_relax(); } while (atomic_read(&dump_lock) != -1); - goto retry; - } - - __dump_stack(); - - if (!was_locked) - atomic_set(&dump_lock, -1); - - local_irq_restore(flags); -} -#else -asmlinkage __visible void dump_stack(void) -{ + printk_cpu_lock_irqsave(flags); __dump_stack(); + printk_cpu_unlock_irqrestore(flags); } -#endif EXPORT_SYMBOL(dump_stack); -- cgit v1.2.3 From 4469c0f17ec63dcc8c9ed512f4330b566c2c0d34 Mon Sep 17 00:00:00 2001 From: Alexander Potapenko Date: Mon, 28 Jun 2021 19:40:30 -0700 Subject: printk: introduce dump_stack_lvl() dump_stack() is used for many different cases, which may require a log level consistent with other kernel messages surrounding the dump_stack() call. Without that, certain systems that are configured to ignore the default level messages will miss stack traces in critical error reports. This patch introduces dump_stack_lvl() that behaves similarly to dump_stack(), but accepts a custom log level. The old dump_stack() becomes equal to dump_stack_lvl(KERN_DEFAULT). A somewhat similar patch has been proposed in 2012: https://lore.kernel.org/lkml/1332493269.2359.9.camel@hebo/ , but wasn't merged. [elver@google.com: add missing dump_stack_lvl() stub if CONFIG_PRINTK=n] Link: https://lkml.kernel.org/r/YJ0KAM0hQev1AmWe@elver.google.com Link: https://lkml.kernel.org/r/20210506105405.3535023-1-glider@google.com Signed-off-by: Alexander Potapenko Reviewed-by: Marco Elver Cc: Petr Mladek Cc: Ingo Molnar Cc: he, bo Cc: Yanmin Zhang Cc: Prasad Sodagudi Cc: Dmitry Vyukov Cc: Sergey Senozhatsky Cc: Steven Rostedt Cc: Andrey Ryabinin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/printk.h | 5 +++++ lib/dump_stack.c | 20 +++++++++++++------- 2 files changed, 18 insertions(+), 7 deletions(-) (limited to 'lib/dump_stack.c') diff --git a/include/linux/printk.h b/include/linux/printk.h index fe7eb2351610..f589b8b60806 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -206,6 +206,7 @@ void __init setup_log_buf(int early); __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...); void dump_stack_print_info(const char *log_lvl); void show_regs_print_info(const char *log_lvl); +extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold; extern asmlinkage void dump_stack(void) __cold; extern void printk_safe_flush(void); extern void printk_safe_flush_on_panic(void); @@ -269,6 +270,10 @@ static inline void show_regs_print_info(const char *log_lvl) { } +static inline void dump_stack_lvl(const char *log_lvl) +{ +} + static inline void dump_stack(void) { } diff --git a/lib/dump_stack.c b/lib/dump_stack.c index f5a33b6f773f..586e3f2c6a15 100644 --- a/lib/dump_stack.c +++ b/lib/dump_stack.c @@ -73,10 +73,10 @@ void show_regs_print_info(const char *log_lvl) dump_stack_print_info(log_lvl); } -static void __dump_stack(void) +static void __dump_stack(const char *log_lvl) { - dump_stack_print_info(KERN_DEFAULT); - show_stack(NULL, NULL, KERN_DEFAULT); + dump_stack_print_info(log_lvl); + show_stack(NULL, NULL, log_lvl); } /** @@ -87,7 +87,7 @@ static void __dump_stack(void) #ifdef CONFIG_SMP static atomic_t dump_lock = ATOMIC_INIT(-1); -asmlinkage __visible void dump_stack(void) +asmlinkage __visible void dump_stack_lvl(const char *log_lvl) { unsigned long flags; int was_locked; @@ -117,7 +117,7 @@ retry: goto retry; } - __dump_stack(); + __dump_stack(log_lvl); if (!was_locked) atomic_set(&dump_lock, -1); @@ -125,9 +125,15 @@ retry: local_irq_restore(flags); } #else -asmlinkage __visible void dump_stack(void) +asmlinkage __visible void dump_stack_lvl(const char *log_lvl) { - __dump_stack(); + __dump_stack(log_lvl); } #endif +EXPORT_SYMBOL(dump_stack_lvl); + +asmlinkage __visible void dump_stack(void) +{ + dump_stack_lvl(KERN_DEFAULT); +} EXPORT_SYMBOL(dump_stack); -- cgit v1.2.3