linux-kernel - Re: [PATCH -v1] acpi: Fix possible recursive locking in hwregs.c

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Date:	Sat, 05 Nov 2011 22:50:48 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-acpi <linux-acpi@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Brown, Len" <len.brown@...el.com>,
	"Moore, Robert" <robert.moore@...el.com>
Subject: Re: [PATCH -v1] acpi: Fix possible recursive locking in hwregs.c

On Fri, 2011-11-04 at 13:53 +0800, Rakib Mullick wrote:
> On Thu, Nov 3, 2011 at 11:40 PM, Srivatsa S. Bhat
> <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> > Hi,
> >
> > On 11/03/2011 05:32 PM, Lin Ming wrote:
> >> On Thu, 2011-11-03 at 18:48 +0800, Rakib Mullick wrote:
> >>> Calling pm-suspend might trigger a recursive lock in it's code path. In function acpi_hw_clear_acpi_status,
> >>
> >> As I replied at https://lkml.org/lkml/2011/9/22/6, I still don't think
> >> there is a recursive lock.
> >>
> >
> > At first look, it definitely doesn't look like a recursive lock, as Lin said.
> > But, quoting Documentation/lockdep-design.txt:
> >
> > "Multi-lock dependency rules:
> > ----------------------------
> >
> > The same lock-class must not be acquired twice, because this could lead
> > to lock recursion deadlocks."
> >
> > So, Rakib, do the 2 locks belong to the same lock-class? If yes, then I think
> > that is the reason for the lockdep splat. Could you show the lockdep warning?
> >
> Yes, same lock-class. And as per "Multi-lock dependency rules:", it
> leads to lock recursion deadlocks.
> Lockdep warning attached.
> 
> > By the way, another way to look at this patch is as an optimization..
> > i.e., if acpi_gbl_hardware_lock doesn't need to be held to call
> > acpi_ev_walk_gpe_list(), then we can move from the coarse-grained locking
> > to finer-grained locking by releasing it earlier, as you did in your patch.
> > [Note that you will have to update the goto label also, i.e., rename it as
> > 'exit' or something like that]
> >
> I can do it, thanks for suggestions. But, what does Lin thinks? Lin
> are you okay?

I'm OK.

We need to figure out why the dead lock happens.
Could you also paste the patch which trigger this dead lock?

Thanks,
Lin Ming

> 
> Thanks,
> Rakib


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