linux-kernel - Re: [PATCH] rcu: Narrow early boot window of illegal synchronous grace periods

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Message-Id: <20170116045622.GK5238@linux.vnet.ibm.com>
Date:   Sun, 15 Jan 2017 20:56:22 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     "Zheng, Lv" <lv.zheng@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "stan.kain@...il.com" <stan.kain@...il.com>,
        "waffolz@...mail.com" <waffolz@...mail.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "mathieu.desnoyers@...icios.com" <mathieu.desnoyers@...icios.com>,
        "jiangshanlai@...il.com" <jiangshanlai@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] rcu: Narrow early boot window of illegal synchronous
 grace periods

On Mon, Jan 16, 2017 at 01:57:25AM +0000, Zheng, Lv wrote:
> Hi,
> 
> > From: Borislav Petkov [mailto:bp@...en8.de]
> > Subject: Re: [PATCH] rcu: Narrow early boot window of illegal synchronous grace periods
> > 
> > On Sat, Jan 14, 2017 at 01:27:40PM +0100, Rafael J. Wysocki wrote:
> > > OK, so this fixes the problem with synchronize_rcu_expedited() in
> > > acpi_os_map_cleanup(), right?
> > 
> > Yeah.
> > 
> > > I wonder if the ACPI-specific fix is still needed, then?
> > 
> > It is not strictly necessary. If you still think it would be better to
> > have it regardless, you could pick it up. I.e., making ACPI more robust,
> > yadda yadda.
> > 
> > I dunno, though, perhaps it is only complicating the code unnecessarily
> > and then can be safely ignored with a mental note for future freezes.
> 
> Glad to see it fixed inside of the API provider.
> 
> IMO, ACPI fix is unnecessary as ACPI is just a user of the RCU APIs.
> And it's pointless to add special checks in the user side in order to use one of them.

With some luck, the RCU patch will go in sooner rather than later.

Should it be delayed for whatever reason, the ACPI patch might well
be needed in the meantime.

							Thanx, Paul