lkml.org 
[lkml]   [2014]   [Dec]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/3] tracepoints: Do not use call_rcu_sched() before early_initcall()
On Sun, Dec 14, 2014 at 12:44:31PM -0500, Steven Rostedt wrote:
> On Sun, 14 Dec 2014 17:29:28 +0000 (UTC)
> Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
>
> > Given that your reason for having this RCU-specific logic in tracepoint.c
> > rather than within call_rcu*() is not slowing down a fast-path, how about
> > creating a new call_rcu_early() and call_rcu_sched_early() which can be
> > called in normal operation and at early boot ?
>
> That's a possibility.
>
> >
> > This would allow us to keep the RCU logic within the RCU implementation
> > rather than strongly coupling it with the tracepoint code.
> >
>
> It's not that strong of a coupling to RCU. It's more coupled to being
> called really early (which needs special care).
>
> It just happened that RCU failed for being called that early. Other
> things could possible fail too (if added to the tracepoint logic).
> Maybe I should rename the variable to "tracepoint_earlyboot" instead.

But you do have to call this quite early. After rcu_init() is invoked,
things should work fine.

> But as RCU is the only thing that failed (so far in my testing), I'll
> think about adding a call_rcu_sched_early(). But then, this does make
> things more complex, and me more nervous about adding it.

I really am nervous about a call_rcu_sched_early() that immediately
invokes the specified callback. That is just begging for someone to
invoke it while traversing a list in an RCU read-side critical section,
which will break.

My thought is to make the compiler initialize the pieces of RCU that
are needed. That said, this initialization includes per-CPU variables,
so the question then becomes "when do per-CPU variables get initialized?"

Thanx, Paul



\
 
 \ /
  Last update: 2014-12-14 19:41    [W:0.038 / U:22.300 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site