Re: [GIT PULL] tracing/NMI/printk: Use seq_buf for safe printing from NMI context

From: Steven Rostedt
Date: Mon Dec 08 2014 - 10:08:59 EST

On Mon, 8 Dec 2014 10:05:28 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> This code solves the issue of performing stack dumps from NMI context.
> The issue is that printk() is not safe from NMI context as if the NMI
> were to trigger when a printk() was being performed, the NMI could
> deadlock from the printk() internal locks. This has been seen in practice.

One added bonus is that this code also makes the NMI dump stack work on
PREEMPT_RT kernels. As printk() includes sleeping locks on PREEMPT_RT,
printk() only writes to console if the console does not use any
rt_mutex converted spin locks. Which a lot do.

-- Steve
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