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author | Sergey Senozhatsky <sergey.senozhatsky@gmail.com> | 2016-12-27 23:16:06 +0900 |
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committer | Petr Mladek <pmladek@suse.com> | 2017-02-08 11:07:11 +0100 |
commit | 099f1c84c0052ec1b27f1c3942eed5830d86bdbb (patch) | |
tree | d24459538b67e6b94b389d7022653c294e510094 /include/linux/printk.h | |
parent | f92bac3b141b8233e34ddf32d227e12bfba07b48 (diff) | |
download | linux-stable-099f1c84c0052ec1b27f1c3942eed5830d86bdbb.tar.gz linux-stable-099f1c84c0052ec1b27f1c3942eed5830d86bdbb.tar.bz2 linux-stable-099f1c84c0052ec1b27f1c3942eed5830d86bdbb.zip |
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.h | 21 |
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; |