Re: [PATCH] tracing: reduce latency and remove percpu trace_seq

[Lai Jiangshan]

Steven Rostedt wrote:

> 
> The "print" in the trace_seq_printf() is the TP_printk() field of the
> TRACE_EVENT. I believe that there were some events (ext4?) that did
> things that required preemption disabled.
> 

It seems that ext4 has no such events.
I find jbd2_dev_to_name() in the TP_printk() field of ext4's tracepoints.
And it seems that jbd2_dev_to_name() requires preemption enabled and sleepable.

Maybe there were some events did things that required preemption disabled.
But No document ensure TP_printk() preemption disabled, such events should
be fixed, I think.
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