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authorSergey Senozhatsky <sergey.senozhatsky@gmail.com>2016-12-27 17:16:06 +0300
committerPetr Mladek <pmladek@suse.com>2017-02-08 13:07:11 +0300
commit099f1c84c0052ec1b27f1c3942eed5830d86bdbb (patch)
treed24459538b67e6b94b389d7022653c294e510094 /include/linux/printk.h
parentf92bac3b141b8233e34ddf32d227e12bfba07b48 (diff)
downloadlinux-099f1c84c0052ec1b27f1c3942eed5830d86bdbb.tar.xz
printk: introduce per-cpu safe_print seq buffer
This patch extends the idea of NMI per-cpu buffers to regions that may cause recursive printk() calls and possible deadlocks. Namely, printk() can't handle printk calls from schedule code or printk() calls from lock debugging code (spin_dump() for instance); because those may be called with `sem->lock' already taken or any other `critical' locks (p->pi_lock, etc.). An example of deadlock can be vprintk_emit() console_unlock() up() << raw_spin_lock_irqsave(&sem->lock, flags); wake_up_process() try_to_wake_up() ttwu_queue() ttwu_activate() activate_task() enqueue_task() enqueue_task_fair() cfs_rq_of() task_of() WARN_ON_ONCE(!entity_is_task(se)) vprintk_emit() console_trylock() down_trylock() raw_spin_lock_irqsave(&sem->lock, flags) ^^^^ deadlock and some other cases. Just like in NMI implementation, the solution uses a per-cpu `printk_func' pointer to 'redirect' printk() calls to a 'safe' callback, that store messages in a per-cpu buffer and flushes them back to logbuf buffer later. Usage example: printk() printk_safe_enter_irqsave(flags) // // any printk() call from here will endup in vprintk_safe(), // that stores messages in a special per-CPU buffer. // printk_safe_exit_irqrestore(flags) The 'redirection' mechanism, though, has been reworked, as suggested by Petr Mladek. Instead of using a per-cpu @print_func callback we now keep a per-cpu printk-context variable and call either default or nmi vprintk function depending on its value. printk_nmi_entrer/exit and printk_safe_enter/exit, thus, just set/celar corresponding bits in printk-context functions. The patch only adds printk_safe support, we don't use it yet. Link: http://lkml.kernel.org/r/20161227141611.940-4-sergey.senozhatsky@gmail.com Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Jan Kara <jack@suse.cz> Cc: Tejun Heo <tj@kernel.org> Cc: Calvin Owens <calvinowens@fb.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'include/linux/printk.h')
-rw-r--r--include/linux/printk.h21
1 files changed, 15 insertions, 6 deletions
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 37e933eeffb2..571257e0f53d 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -147,17 +147,11 @@ void early_printk(const char *s, ...) { }
#endif
#ifdef CONFIG_PRINTK_NMI
-extern void printk_safe_init(void);
extern void printk_nmi_enter(void);
extern void printk_nmi_exit(void);
-extern void printk_safe_flush(void);
-extern void printk_safe_flush_on_panic(void);
#else
-static inline void printk_safe_init(void) { }
static inline void printk_nmi_enter(void) { }
static inline void printk_nmi_exit(void) { }
-static inline void printk_safe_flush(void) { }
-static inline void printk_safe_flush_on_panic(void) { }
#endif /* PRINTK_NMI */
#ifdef CONFIG_PRINTK
@@ -209,6 +203,9 @@ 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 void printk_safe_init(void);
+extern void printk_safe_flush(void);
+extern void printk_safe_flush_on_panic(void);
#else
static inline __printf(1, 0)
int vprintk(const char *s, va_list args)
@@ -268,6 +265,18 @@ static inline void dump_stack_print_info(const char *log_lvl)
static inline void show_regs_print_info(const char *log_lvl)
{
}
+
+static inline void printk_safe_init(void)
+{
+}
+
+static inline void printk_safe_flush(void)
+{
+}
+
+static inline void printk_safe_flush_on_panic(void)
+{
+}
#endif
extern asmlinkage void dump_stack(void) __cold;