Messages in this thread Patch in this message | | | From | Sergey Senozhatsky <> | Subject | [RFC][PATCH] printk: do not call console drivers from printk_safe context | Date | Tue, 24 Apr 2018 11:28:02 +0900 |
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Calling console drivers from printk_safe() context does not really make call_console_drivers() any safer, because printk_safe() has nothing to do with console drivers or the underlying code. At the same time printk()-s from console drivers are fine, they don't deadlock the system. We need printk_safe() because of the way vprintk_emit() works -- we protect logbuf lock, console_owner_lock and console_sem spin_lock with printk_safe, -- not because of the console drivers (which don't deal with logbuf, console_owner_lock or console_sem locks). Hence we can call console drivers outside of printk_safe() context.
Another thing to notice is that, printk_safe() introduces unneeded complexity, since any printk() message from console drivers has to be stored in per-CPU printk_safe() buffer first, then be flushed via IRQ work: call_console_drivers() printk() printk_safe_log_store() IRQ_work() printk_safe_flush_buffer() printk_deferred() log_store() irq_work_queue() * wake_up_klogd_work_func() *
Note that this also costs us extra IRQ work [along with the IRQ work that flushes printk_safe() buffer] - we flush per-CPU printk_safe() buffers via printk_deferred().
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> --- kernel/printk/internal.h | 7 ++++++- kernel/printk/printk.c | 2 ++ 2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 2a7d04049af4..f3ba1bf08590 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -55,8 +55,13 @@ void __printk_safe_exit(void); } while (0) #else +static void __printk_safe_enter(void) {} +static void __printk_safe_exit(void) {} -__printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; } +static __printf(1, 0) int vprintk_func(const char *fmt, va_list args) +{ + return 0; +} /* * In !PRINTK builds we still export logbuf_lock spin_lock, console_sem diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 2f4af216bd6e..9acb25ce6081 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2391,9 +2391,11 @@ void console_unlock(void) */ console_lock_spinning_enable(); + __printk_safe_exit(); stop_critical_timings(); /* don't trace print latency */ call_console_drivers(ext_text, ext_len, text, len); start_critical_timings(); + __printk_safe_enter(); if (console_lock_spinning_disable_and_check()) { printk_safe_exit_irqrestore(flags); -- 2.17.0
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