Re: BUG: ib_mad ftrace event unsupported migration

[Steven Rostedt]

On Wed, 2 Nov 2022 22:01:17 +0200
Leonid Ravich <lravich@xxxxxxxxx> wrote:

> disagree, without CONFIG_PREEMPTION (which is the default case in some
> destros) we will not get any warning, because there will not be
> preamption disable.

I test all for my code (NON_PREEMPT, VOLUNTEER_PREEMPT, PREEMPT) and
with and without lockdep enabled.

This would be a bug if you called kmalloc(X, GFP_KERNEL) in *any* non
preempt section.

> 
> second issue I see and maybe it is only me, is that the assuption of
> atomicity in trace is not a common knowledge for trace users.     

Well, I suppose we could add more documentation. Would that help? Where
would you see it? In the sample code?

I advise not even grabbing locks in trace events, because in most cases
lockdep will not catch any issues with them (it will be hidden unless
the trace event is enabled).

-- Steve