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>
This commit is contained in:
Sergey Senozhatsky
Petr Mladek
parent
f92bac3b14
commit
099f1c84c0
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@ -147,17 +147,11 @@ void early_printk(const char *s, ...) { }
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#endif
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#ifdef CONFIG_PRINTK_NMI
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extern void printk_safe_init(void);
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extern void printk_nmi_enter(void);
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extern void printk_nmi_exit(void);
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extern void printk_safe_flush(void);
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extern void printk_safe_flush_on_panic(void);
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#else
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static inline void printk_safe_init(void) { }
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static inline void printk_nmi_enter(void) { }
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static inline void printk_nmi_exit(void) { }
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static inline void printk_safe_flush(void) { }
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static inline void printk_safe_flush_on_panic(void) { }
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#endif /* PRINTK_NMI */
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#ifdef CONFIG_PRINTK
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@ -209,6 +203,9 @@ void __init setup_log_buf(int early);
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__printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...);
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void dump_stack_print_info(const char *log_lvl);
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void show_regs_print_info(const char *log_lvl);
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extern void printk_safe_init(void);
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extern void printk_safe_flush(void);
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extern void printk_safe_flush_on_panic(void);
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#else
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static inline __printf(1, 0)
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int vprintk(const char *s, va_list args)
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@ -268,6 +265,18 @@ static inline void dump_stack_print_info(const char *log_lvl)
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static inline void show_regs_print_info(const char *log_lvl)
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{
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}
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static inline void printk_safe_init(void)
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{
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}
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static inline void printk_safe_flush(void)
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{
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}
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static inline void printk_safe_flush_on_panic(void)
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{
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}
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#endif
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extern asmlinkage void dump_stack(void) __cold;
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@ -1,3 +1,3 @@
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obj-y = printk.o
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obj-$(CONFIG_PRINTK_NMI) += printk_safe.o
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obj-$(CONFIG_PRINTK) += printk_safe.o
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obj-$(CONFIG_A11Y_BRAILLE_CONSOLE) += braille.o
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@ -16,26 +16,8 @@
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*/
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#include <linux/percpu.h>
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typedef __printf(1, 0) int (*printk_func_t)(const char *fmt, va_list args);
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int __printf(1, 0) vprintk_default(const char *fmt, va_list args);
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#ifdef CONFIG_PRINTK_NMI
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extern raw_spinlock_t logbuf_lock;
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/*
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* printk() could not take logbuf_lock in NMI context. Instead,
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* it temporary stores the strings into a per-CPU buffer.
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* The alternative implementation is chosen transparently
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* via per-CPU variable.
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*/
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DECLARE_PER_CPU(printk_func_t, printk_func);
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static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
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{
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return this_cpu_read(printk_func)(fmt, args);
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}
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extern atomic_t nmi_message_lost;
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static inline int get_nmi_message_lost(void)
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{
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@ -44,14 +26,62 @@ static inline int get_nmi_message_lost(void)
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#else /* CONFIG_PRINTK_NMI */
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static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
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{
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return vprintk_default(fmt, args);
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}
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static inline int get_nmi_message_lost(void)
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{
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return 0;
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}
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#endif /* CONFIG_PRINTK_NMI */
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#ifdef CONFIG_PRINTK
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#define PRINTK_SAFE_CONTEXT_MASK 0x7fffffff
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#define PRINTK_NMI_CONTEXT_MASK 0x80000000
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extern raw_spinlock_t logbuf_lock;
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__printf(1, 0) int vprintk_default(const char *fmt, va_list args);
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__printf(1, 0) int vprintk_func(const char *fmt, va_list args);
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void __printk_safe_enter(void);
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void __printk_safe_exit(void);
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#define printk_safe_enter_irqsave(flags) \
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do { \
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local_irq_save(flags); \
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__printk_safe_enter(); \
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} while (0)
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#define printk_safe_exit_irqrestore(flags) \
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do { \
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__printk_safe_exit(); \
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local_irq_restore(flags); \
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} while (0)
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#define printk_safe_enter_irq() \
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do { \
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local_irq_disable(); \
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__printk_safe_enter(); \
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} while (0)
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#define printk_safe_exit_irq() \
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do { \
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__printk_safe_exit(); \
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local_irq_enable(); \
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} while (0)
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#else
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__printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; }
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/*
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* In !PRINTK builds we still export logbuf_lock spin_lock, console_sem
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* semaphore and some of console functions (console_unlock()/etc.), so
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* printk-safe must preserve the existing local IRQ guarantees.
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*/
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#define printk_safe_enter_irqsave(flags) local_irq_save(flags)
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#define printk_safe_exit_irqrestore(flags) local_irq_restore(flags)
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#define printk_safe_enter_irq() local_irq_disable()
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#define printk_safe_exit_irq() local_irq_enable()
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#endif /* CONFIG_PRINTK */
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@ -1902,9 +1902,6 @@ static size_t msg_print_text(const struct printk_log *msg,
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bool syslog, char *buf, size_t size) { return 0; }
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static bool suppress_message_printing(int level) { return false; }
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/* Still needs to be defined for users */
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DEFINE_PER_CPU(printk_func_t, printk_func);
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#endif /* CONFIG_PRINTK */
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#ifdef CONFIG_EARLY_PRINTK
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@ -1,5 +1,5 @@
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/*
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* printk_safe.c - Safe printk in NMI context
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* printk_safe.c - Safe printk for printk-deadlock-prone contexts
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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@ -32,13 +32,13 @@
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* is later flushed into the main ring buffer via IRQ work.
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*
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* The alternative implementation is chosen transparently
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* via @printk_func per-CPU variable.
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* by examinig current printk() context mask stored in @printk_context
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* per-CPU variable.
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*
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* The implementation allows to flush the strings also from another CPU.
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* There are situations when we want to make sure that all buffers
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* were handled or when IRQs are blocked.
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*/
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DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default;
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static int printk_safe_irq_ready;
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atomic_t nmi_message_lost;
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@ -50,18 +50,28 @@ struct printk_safe_seq_buf {
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struct irq_work work; /* IRQ work that flushes the buffer */
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unsigned char buffer[SAFE_LOG_BUF_LEN];
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};
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static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
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static DEFINE_PER_CPU(int, printk_context);
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#ifdef CONFIG_PRINTK_NMI
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static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
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#endif
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/*
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* Safe printk() for NMI context. It uses a per-CPU buffer to
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* store the message. NMIs are not nested, so there is always only
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* one writer running. But the buffer might get flushed from another
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* CPU, so we need to be careful.
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* Add a message to per-CPU context-dependent buffer. NMI and printk-safe
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* have dedicated buffers, because otherwise printk-safe preempted by
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* NMI-printk would have overwritten the NMI messages.
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*
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* The messages are fushed from irq work (or from panic()), possibly,
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* from other CPU, concurrently with printk_safe_log_store(). Should this
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* happen, printk_safe_log_store() will notice the buffer->len mismatch
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* and repeat the write.
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*/
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static int vprintk_nmi(const char *fmt, va_list args)
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static int printk_safe_log_store(struct printk_safe_seq_buf *s,
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const char *fmt, va_list args)
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{
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struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
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int add = 0;
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int add;
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size_t len;
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again:
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@ -74,8 +84,8 @@ again:
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}
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/*
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* Make sure that all old data have been read before the buffer was
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* reseted. This is not needed when we just append data.
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* Make sure that all old data have been read before the buffer
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* was reset. This is not needed when we just append data.
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*/
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if (!len)
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smp_rmb();
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@ -161,7 +171,7 @@ static int printk_safe_flush_buffer(const char *start, size_t len)
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}
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/*
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* Flush data from the associated per_CPU buffer. The function
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* Flush data from the associated per-CPU buffer. The function
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* can be called either via IRQ work or independently.
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*/
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static void __printk_safe_flush(struct irq_work *work)
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@ -231,8 +241,12 @@ void printk_safe_flush(void)
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{
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int cpu;
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for_each_possible_cpu(cpu)
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for_each_possible_cpu(cpu) {
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#ifdef CONFIG_PRINTK_NMI
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__printk_safe_flush(&per_cpu(nmi_print_seq, cpu).work);
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#endif
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__printk_safe_flush(&per_cpu(safe_print_seq, cpu).work);
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}
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}
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/**
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@ -262,14 +276,88 @@ void printk_safe_flush_on_panic(void)
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printk_safe_flush();
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}
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#ifdef CONFIG_PRINTK_NMI
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/*
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* Safe printk() for NMI context. It uses a per-CPU buffer to
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* store the message. NMIs are not nested, so there is always only
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* one writer running. But the buffer might get flushed from another
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* CPU, so we need to be careful.
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*/
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static int vprintk_nmi(const char *fmt, va_list args)
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{
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struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
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return printk_safe_log_store(s, fmt, args);
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}
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void printk_nmi_enter(void)
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{
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this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
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}
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void printk_nmi_exit(void)
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{
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this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
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}
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#else
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static int vprintk_nmi(const char *fmt, va_list args)
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{
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return 0;
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}
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#endif /* CONFIG_PRINTK_NMI */
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/*
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* Lock-less printk(), to avoid deadlocks should the printk() recurse
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* into itself. It uses a per-CPU buffer to store the message, just like
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* NMI.
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*/
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static int vprintk_safe(const char *fmt, va_list args)
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{
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struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq);
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return printk_safe_log_store(s, fmt, args);
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}
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/* Can be preempted by NMI. */
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void __printk_safe_enter(void)
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{
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this_cpu_inc(printk_context);
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}
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/* Can be preempted by NMI. */
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void __printk_safe_exit(void)
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{
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this_cpu_dec(printk_context);
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}
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__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
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{
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if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
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return vprintk_nmi(fmt, args);
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if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)
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return vprintk_safe(fmt, args);
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return vprintk_default(fmt, args);
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}
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void __init printk_safe_init(void)
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{
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int cpu;
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for_each_possible_cpu(cpu) {
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struct printk_safe_seq_buf *s = &per_cpu(nmi_print_seq, cpu);
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struct printk_safe_seq_buf *s;
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s = &per_cpu(safe_print_seq, cpu);
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init_irq_work(&s->work, __printk_safe_flush);
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#ifdef CONFIG_PRINTK_NMI
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s = &per_cpu(nmi_print_seq, cpu);
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init_irq_work(&s->work, __printk_safe_flush);
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#endif
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}
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/* Make sure that IRQ works are initialized before enabling. */
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@ -279,13 +367,3 @@ void __init printk_safe_init(void)
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/* Flush pending messages that did not have scheduled IRQ works. */
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printk_safe_flush();
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}
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void printk_nmi_enter(void)
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{
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this_cpu_write(printk_func, vprintk_nmi);
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}
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void printk_nmi_exit(void)
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{
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this_cpu_write(printk_func, vprintk_default);
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}
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