Messages in this thread Patch in this message | | | From | Sergey Senozhatsky <> | Subject | [PATCH] printk: use console_trylock() in console_cpu_notify() | Date | Sat, 21 Jan 2017 19:47:29 +0900 |
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There is no need to always call blocking console_lock() in console_cpu_notify(), it's quite possible that console_sem can be locked by other CPU on the system, either already printing or soon to begin printing the messages. console_lock() in this case can simply block CPU hotplug for unknown period of time (console_unlock() is time unbound). Not that hotplug is very fast, but still, with other CPUs being online and doing printk() console_cpu_notify() can stuck.
Use console_trylock() instead and opt-out if console_sem is already acquired from another CPU, since that CPU will do the printing for us.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> --- kernel/printk/printk.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 7180088cbb23..772eb16436ce 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2028,15 +2028,16 @@ void resume_console(void) * @cpu: unused * * If printk() is called from a CPU that is not online yet, the messages - * will be spooled but will not show up on the console. This function is - * called when a new CPU comes online (or fails to come up), and ensures - * that any such output gets printed. + * will be printed on the console only if there are CON_ANYTIME consoles. + * This function is called when a new CPU comes online (or fails to come + * up) or goes offline. */ static int console_cpu_notify(unsigned int cpu) { if (!cpuhp_tasks_frozen) { - console_lock(); - console_unlock(); + /* If trylock fails, someone else is doing the printing */ + if (console_trylock()) + console_unlock(); } return 0; } -- 2.11.0
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