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

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Date:	Thu, 22 Sep 2011 12:28:07 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Brown, Len" <len.brown@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"Moore, Robert" <robert.moore@...el.com>
Subject: Re: [PATCH] acpi: Fix possible recursive locking in hwregs.c

On Thu, 2011-09-22 at 11:35 +0800, Rakib Mullick wrote:
> On Thu, Sep 22, 2011 at 6:59 AM, Lin Ming <ming.m.lin@...el.com> wrote:
> > On Thu, Sep 22, 2011 at 2:09 AM, Rakib Mullick <rakib.mullick@...il.com> wrote:
> >> Calling pm-suspend might trigger a recursive lock in it's code path. In function acpi_hw_clear_acpi_status,
> >> acpi_os_release_lock holds the lock acpi_gbl_hardware_lock before calling acpi_hw_register_write(), then
> >> without releasing acpi_gbl_hardware_lock, this function calls acpi_ev_walk_gpe_list, which also tries to
> >> hold acpi_gbl_hardware_lock and thus causes possible recursive lock.
> >
> > No, acpi_ev_walk_gpe_list holds acpi_gbl_gpe_lock.
> >
> Yes, right. Actually, acpi_os_release_lock() tries to hold
> acpi_gbl_gpe_lock without releasing acpi_gbl_hardware_lock. Right?

Do you mean "acpi_ev_walk_gpe_list() tries to hold
acpi_gbl_gpe_lock..."?

We have below locks sequence. I don't see the problem.

acpi_hw_clear_acpi_status:

     <acquire acpi_gbl_hardware_lock>

         acpi_ev_walk_gpe_list:
             <acquire acpi_gbl_gpe_lock>
             ...
             <release acpi_gbl_gpe_lock>
         ...
     <release acpi_gbl_hardware_lock>

> 
> Thanks,
> Rakib


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