linux-kernel - Re: 174cc7187e6f ACPICA: Tables: Back port acpi_get_table_with_size() and early_acpi_os_unmap

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Date:   Wed, 11 Jan 2017 01:51:56 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Zheng, Lv" <lv.zheng@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Moore, Robert" <robert.moore@...el.com>,
        J?rg R?del <joro@...tes.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: 174cc7187e6f ACPICA: Tables: Back port
 acpi_get_table_with_size() and early_acpi_os_unmap_memory() from Linux
 kernel

On Wed, Jan 11, 2017 at 10:21:06AM +0100, Borislav Petkov wrote:
> On Mon, Jan 09, 2017 at 09:51:29PM -0800, Paul E. McKenney wrote:
> > Definitely.
> 
> Btw, we have more breakage from RCU expedited using workqueues:
> https://bugzilla.kernel.org/show_bug.cgi?id=192111
> 
> I've added you to CC but let me have other bug reporters confirm reverting
> 
>   8b355e3bc140 ("rcu: Drive expedited grace periods from workqueue")
> 
> does fix the issue for them too.

Yes, you could make RCU expedited grace periods go back to using the
requesting task, and that would allow expedited grace periods to run early
in the boot process.  But that causes problems with signals and the like
unless you revert a few other patches.  The bugzilla is interesting --
it looks like ACPI was in some cases doing early-boot grace-period waits
some time back?

I have a limping prototype RCU patch that should avoid this problem.

If all goes well, I will send it out late tomorrow evening, Pacific Time.

							Thanx, Paul