On 2019-03-04, Sergey Senozhatsky <[email protected]> wrote: >> + /* the printk kthread never exits */ >> + for (;;) { >> + ret = prb_iter_wait_next(&iter, buf, >> + PRINTK_RECORD_MAX, &master_seq); >> + if (ret == -ERESTARTSYS) { >> + continue; >> + } else if (ret < 0) { >> + /* iterator invalid, start over */ >> + prb_iter_init(&iter, &printk_rb, NULL); >> + continue; >> + } >> + >> + msg = (struct printk_log *)buf; >> + format_text(msg, master_seq, ext_text, &ext_len, text, >> + &len, printk_time); >> + >> + console_lock(); >> + if (len > 0 || ext_len > 0) { >> + call_console_drivers(ext_text, ext_len, text, len); >> + boot_delay_msec(msg->level); >> + printk_delay(); >> + } >> + console_unlock(); >> + } > > This, theoretically, creates a whole new world of possibilities for > console drivers. Now they can do GFP_KERNEL allocations and stall > printk_kthread during OOM; or they can explicitly reschedule from > ->write() callback (via console_conditional_schedule()) because > console_lock() sets console_may_schedule.
This was the intention. Although, as I mentioned in a previous response[0], perhaps we should not loosen the requirements on write(). > It's one thing to do cond_resched() (or to let preemption to take > over) after call_console_drivers() (when we are done printing a > message to all console drivers) and another thing to let preemption to > take over while we are printing a messages to the consoles. It > probably would make sense to disable preemption around > call_console_drivers(). I could see disabling preemption and interrupts for emergency messages in the printk-kthread in order to synchronize against an irq_work secondary printer as suggested in my response[0]. But I don't see an advantage to disabling preemption in general for call_console_drivers(). It is exactly that disable_preempt() that is so harmful for realtime tasks. John Ogness [0] https://lkml.kernel.org/r/[email protected]
