[PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[Krzysztof Hałasa]

Many ARM platforms use a wrapper:
/*
 * Compatibility wrapper for older platforms that do not care about
 * passing the parent device.
 */
static inline void pci_common_init(struct hw_pci *hw)
{
        pci_common_init_dev(NULL, hw);
}

which means that pci_bus_assign_domain_nr() can be called without
a parent. This patch fixes the NULL pointer dereference.

Signed-off-by: Krzysztof Hałasa <khalasa@piap.pl>
Cc: stable@vger.kernel.org

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 602eb42..f89db3a 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4772,8 +4772,10 @@ int pci_get_new_domain_nr(void)
 void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
 {
 	static int use_dt_domains = -1;
-	int domain = of_get_pci_domain_nr(parent->of_node);
+	int domain = -1;
 
+	if (parent)
+		domain = of_get_pci_domain_nr(parent->of_node);
 	/*
 	 * Check DT domain and use_dt_domains values.
 	 *

-- 
Krzysztof Halasa

Industrial Research Institute for Automation and Measurements PIAP
Al. Jerozolimskie 202, 02-486 Warsaw, Poland

Re: [PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[Bjorn Helgaas]

Hi Krzysztof,

On Tue, Mar 01, 2016 at 07:07:18AM +0100, Krzysztof Hałasa wrote:
> Many ARM platforms use a wrapper:
> /*
>  * Compatibility wrapper for older platforms that do not care about
>  * passing the parent device.
>  */
> static inline void pci_common_init(struct hw_pci *hw)
> {
>         pci_common_init_dev(NULL, hw);
> }
> 
> which means that pci_bus_assign_domain_nr() can be called without
> a parent. This patch fixes the NULL pointer dereference.

What exactly is the impact of this?  Does this fix need to be in v4.5?
It sounds like it should be, but I need a little more detailed
justification, e.g., "platforms X, Y, Z don't boot at all without
this change."

> Signed-off-by: Krzysztof Hałasa <khalasa@piap.pl>
> Cc: stable@vger.kernel.org
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 602eb42..f89db3a 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4772,8 +4772,10 @@ int pci_get_new_domain_nr(void)
>  void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
>  {
>  	static int use_dt_domains = -1;
> -	int domain = of_get_pci_domain_nr(parent->of_node);
> +	int domain = -1;
>  
> +	if (parent)
> +		domain = of_get_pci_domain_nr(parent->of_node);
>  	/*
>  	 * Check DT domain and use_dt_domains values.
>  	 *
> 
> -- 
> Krzysztof Halasa
> 
> Industrial Research Institute for Automation and Measurements PIAP
> Al. Jerozolimskie 202, 02-486 Warsaw, Poland

Re: [PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[Krzysztof Hałasa]

Hi Bjorn,

Bjorn Helgaas <helgaas@kernel.org> writes:

> On Tue, Mar 01, 2016 at 07:07:18AM +0100, Krzysztof Hałasa wrote:
>> Many ARM platforms use a wrapper:
>> /*
>>  * Compatibility wrapper for older platforms that do not care about
>>  * passing the parent device.
>>  */
>> static inline void pci_common_init(struct hw_pci *hw)
>> {
>>         pci_common_init_dev(NULL, hw);
>> }
>> 
>> which means that pci_bus_assign_domain_nr() can be called without
>> a parent. This patch fixes the NULL pointer dereference.
>
> What exactly is the impact of this?  Does this fix need to be in v4.5?
> It sounds like it should be, but I need a little more detailed
> justification, e.g., "platforms X, Y, Z don't boot at all without
> this change."

At least CNS3xxx doesn't boot. I haven't verified a couple of others,
but they may be broken as well.
-- 
Krzysztof Halasa

Industrial Research Institute for Automation and Measurements PIAP
Al. Jerozolimskie 202, 02-486 Warsaw, Poland

Re: [PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[Bjorn Helgaas]

On Fri, Mar 04, 2016 at 07:13:49AM +0100, Krzysztof Hałasa wrote:
> Hi Bjorn,
> 
> Bjorn Helgaas <helgaas@kernel.org> writes:
> 
> > On Tue, Mar 01, 2016 at 07:07:18AM +0100, Krzysztof Hałasa wrote:
> >> Many ARM platforms use a wrapper:
> >> /*
> >>  * Compatibility wrapper for older platforms that do not care about
> >>  * passing the parent device.
> >>  */
> >> static inline void pci_common_init(struct hw_pci *hw)
> >> {
> >>         pci_common_init_dev(NULL, hw);
> >> }
> >> 
> >> which means that pci_bus_assign_domain_nr() can be called without
> >> a parent. This patch fixes the NULL pointer dereference.
> >
> > What exactly is the impact of this?  Does this fix need to be in v4.5?
> > It sounds like it should be, but I need a little more detailed
> > justification, e.g., "platforms X, Y, Z don't boot at all without
> > this change."
> 
> At least CNS3xxx doesn't boot. I haven't verified a couple of others,
> but they may be broken as well.

Good, thanks.  Also (I should have asked this before), please include a
"Fixes:" line so we know exactly when this broke and what stable kernels
need the fix.

Bjorn

Re: [PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[Krzysztof Hałasa]

Bjorn Helgaas <helgaas@kernel.org> writes:

>> At least CNS3xxx doesn't boot. I haven't verified a couple of others,
>> but they may be broken as well.
>
> Good, thanks.  Also (I should have asked this before), please include a
> "Fixes:" line so we know exactly when this broke and what stable kernels
> need the fix.

The problem started here:

Fixes: 8c7d14746abc ("ARM/PCI: Move to generic PCI domains")

It means the patch should be applicable starting with v4.0, and ...
indeed v4.0 with the patch boots correctly, while v4.0 without the patch
does not.

Thanks.
-- 
Krzysztof Halasa

Industrial Research Institute for Automation and Measurements PIAP
Al. Jerozolimskie 202, 02-486 Warsaw, Poland

Re: [PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[Bjorn Helgaas]

[+cc Lorenzo]

On Tue, Mar 01, 2016 at 07:07:18AM +0100, Krzysztof Hałasa wrote:
> Many ARM platforms use a wrapper:
> /*
>  * Compatibility wrapper for older platforms that do not care about
>  * passing the parent device.
>  */
> static inline void pci_common_init(struct hw_pci *hw)
> {
>         pci_common_init_dev(NULL, hw);
> }
> 
> which means that pci_bus_assign_domain_nr() can be called without
> a parent. This patch fixes the NULL pointer dereference.
> 
> Signed-off-by: Krzysztof Hałasa <khalasa@piap.pl>
> Cc: stable@vger.kernel.org

I applied this to for-linus with changelog as below for v4.5, thanks!

Wow, this is terrible.  All ARM32 systems that use pci_common_init()
crash at boot.  That includes cns3xxx, dove, footbridge, iopl13xx,
ip32x, iop33x, ixp4xx, ks8695, mv78xx0, orion5x, pxa, sa1100, etc.
Apparently they've been crashing since v4.0, when 7c674700098c and
8c7d14746abc appeared.  I can hardly believe nobody noticed until now.

Actually, I did find one problem report:
http://forum.doozan.com/read.php?2,17868,22070,quote=1 from last May,
but apparently it got lost in a forum and never found its way
upstream.

I reworked the changelog because this problem will affect *any* arch
that enables CONFIG_PCI_DOMAINS_GENERIC and supplies NULL "parent"
pointers -- ia64, mips, mn10300, s390, x86, etc., would be affected if
they enabled CONFIG_PCI_DOMAINS_GENERIC.

I also added a "Fixes:" tag for 7c674700098c, since that's the commit
that added the generic code we're fixing.  Backports of 7c674700098c
should also backport this change.

Bjorn



commit 71babd2a89fe
Author: Krzysztof =?utf-8?Q?Ha=C5=82asa?= <khalasa@piap.pl>
Date:   Tue Mar 1 07:07:18 2016 +0100

    PCI: Allow a NULL "parent" pointer in pci_bus_assign_domain_nr()
    
    pci_create_root_bus() passes a "parent" pointer to
    pci_bus_assign_domain_nr().  When CONFIG_PCI_DOMAINS_GENERIC is defined,
    pci_bus_assign_domain_nr() dereferences that pointer.  Many callers of
    pci_create_root_bus() supply a NULL "parent" pointer, which leads to a NULL
    pointer dereference error.
    
    7c674700098c ("PCI: Move domain assignment from arm64 to generic code")
    moved the "parent" dereference from arm64 to generic code.  Only arm64 used
    that code (because only arm64 defined CONFIG_PCI_DOMAINS_GENERIC), and it
    always supplied a valid "parent" pointer.  Other arches supplied NULL
    "parent" pointers but didn't defined CONFIG_PCI_DOMAINS_GENERIC, so they
    used a no-op version of pci_bus_assign_domain_nr().
    
    8c7d14746abc ("ARM/PCI: Move to generic PCI domains") defined
    CONFIG_PCI_DOMAINS_GENERIC on ARM, and many ARM platforms use
    pci_common_init(), which supplies a NULL "parent" pointer.
    These platforms (cns3xxx, dove, footbridge, iop13xx, etc.) crash
    with a NULL pointer dereference like this while probing PCI:
    
      Unable to handle kernel NULL pointer dereference at virtual address 000000a4
      PC is at pci_bus_assign_domain_nr+0x10/0x84
      LR is at pci_create_root_bus+0x48/0x2e4
      Kernel panic - not syncing: Attempted to kill init!
    
    [bhelgaas: changelog, add "Reported:" and "Fixes:" tags]
    Reported: http://forum.doozan.com/read.php?2,17868,22070,quote=1
    Fixes: 8c7d14746abc ("ARM/PCI: Move to generic PCI domains")
    Fixes: 7c674700098c ("PCI: Move domain assignment from arm64 to generic code")
    Signed-off-by: Krzysztof Hałasa <khalasa@piap.pl>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    CC: stable@vger.kernel.org	# v4.0+

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 602eb42..f89db3a 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4772,8 +4772,10 @@ int pci_get_new_domain_nr(void)
 void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
 {
 	static int use_dt_domains = -1;
-	int domain = of_get_pci_domain_nr(parent->of_node);
+	int domain = -1;
 
+	if (parent)
+		domain = of_get_pci_domain_nr(parent->of_node);
 	/*
 	 * Check DT domain and use_dt_domains values.
 	 *

Re: [PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[Lorenzo Pieralisi]

On Mon, Mar 07, 2016 at 04:33:11PM -0600, Bjorn Helgaas wrote:
> [+cc Lorenzo]
> 
> On Tue, Mar 01, 2016 at 07:07:18AM +0100, Krzysztof Ha??asa wrote:
> > Many ARM platforms use a wrapper:
> > /*
> >  * Compatibility wrapper for older platforms that do not care about
> >  * passing the parent device.
> >  */
> > static inline void pci_common_init(struct hw_pci *hw)
> > {
> >         pci_common_init_dev(NULL, hw);
> > }
> > 
> > which means that pci_bus_assign_domain_nr() can be called without
> > a parent. This patch fixes the NULL pointer dereference.
> > 
> > Signed-off-by: Krzysztof Ha??asa <khalasa@piap.pl>
> > Cc: stable@vger.kernel.org
> 
> I applied this to for-linus with changelog as below for v4.5, thanks!
> 
> Wow, this is terrible.  All ARM32 systems that use pci_common_init()
> crash at boot.  That includes cns3xxx, dove, footbridge, iopl13xx,
> ip32x, iop33x, ixp4xx, ks8695, mv78xx0, orion5x, pxa, sa1100, etc.
> Apparently they've been crashing since v4.0, when 7c674700098c and
> 8c7d14746abc appeared.  I can hardly believe nobody noticed until now.
> 
> Actually, I did find one problem report:
> http://forum.doozan.com/read.php?2,17868,22070,quote=1 from last May,
> but apparently it got lost in a forum and never found its way
> upstream.
> 
> I reworked the changelog because this problem will affect *any* arch
> that enables CONFIG_PCI_DOMAINS_GENERIC and supplies NULL "parent"
> pointers -- ia64, mips, mn10300, s390, x86, etc., would be affected if
> they enabled CONFIG_PCI_DOMAINS_GENERIC.
> 
> I also added a "Fixes:" tag for 7c674700098c, since that's the commit
> that added the generic code we're fixing.  Backports of 7c674700098c
> should also backport this change.

That's really unfortunate, when I moved code from arm64 to generic I
did not spot this issue in the original code and carried it over, you
summarized the reasons in the commit log so without any further ado (and
with my apologies):

Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

> 
> Bjorn
> 
> 
> 
> commit 71babd2a89fe
> Author: Krzysztof =?utf-8?Q?Ha=C5=82asa?= <khalasa@piap.pl>
> Date:   Tue Mar 1 07:07:18 2016 +0100
> 
>     PCI: Allow a NULL "parent" pointer in pci_bus_assign_domain_nr()
>     
>     pci_create_root_bus() passes a "parent" pointer to
>     pci_bus_assign_domain_nr().  When CONFIG_PCI_DOMAINS_GENERIC is defined,
>     pci_bus_assign_domain_nr() dereferences that pointer.  Many callers of
>     pci_create_root_bus() supply a NULL "parent" pointer, which leads to a NULL
>     pointer dereference error.
>     
>     7c674700098c ("PCI: Move domain assignment from arm64 to generic code")
>     moved the "parent" dereference from arm64 to generic code.  Only arm64 used
>     that code (because only arm64 defined CONFIG_PCI_DOMAINS_GENERIC), and it
>     always supplied a valid "parent" pointer.  Other arches supplied NULL
>     "parent" pointers but didn't defined CONFIG_PCI_DOMAINS_GENERIC, so they
>     used a no-op version of pci_bus_assign_domain_nr().
>     
>     8c7d14746abc ("ARM/PCI: Move to generic PCI domains") defined
>     CONFIG_PCI_DOMAINS_GENERIC on ARM, and many ARM platforms use
>     pci_common_init(), which supplies a NULL "parent" pointer.
>     These platforms (cns3xxx, dove, footbridge, iop13xx, etc.) crash
>     with a NULL pointer dereference like this while probing PCI:
>     
>       Unable to handle kernel NULL pointer dereference at virtual address 000000a4
>       PC is at pci_bus_assign_domain_nr+0x10/0x84
>       LR is at pci_create_root_bus+0x48/0x2e4
>       Kernel panic - not syncing: Attempted to kill init!
>     
>     [bhelgaas: changelog, add "Reported:" and "Fixes:" tags]
>     Reported: http://forum.doozan.com/read.php?2,17868,22070,quote=1
>     Fixes: 8c7d14746abc ("ARM/PCI: Move to generic PCI domains")
>     Fixes: 7c674700098c ("PCI: Move domain assignment from arm64 to generic code")
>     Signed-off-by: Krzysztof Ha??asa <khalasa@piap.pl>
>     Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>     CC: stable@vger.kernel.org	# v4.0+
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 602eb42..f89db3a 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4772,8 +4772,10 @@ int pci_get_new_domain_nr(void)
>  void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
>  {
>  	static int use_dt_domains = -1;
> -	int domain = of_get_pci_domain_nr(parent->of_node);
> +	int domain = -1;
>  
> +	if (parent)
> +		domain = of_get_pci_domain_nr(parent->of_node);
>  	/*
>  	 * Check DT domain and use_dt_domains values.
>  	 *
> 

Re: [PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[Bjorn Helgaas]

On Tue, Mar 08, 2016 at 03:01:20AM +0000, Lorenzo Pieralisi wrote:
> On Mon, Mar 07, 2016 at 04:33:11PM -0600, Bjorn Helgaas wrote:
> > [+cc Lorenzo]
> > 
> > On Tue, Mar 01, 2016 at 07:07:18AM +0100, Krzysztof Ha??asa wrote:
> > > Many ARM platforms use a wrapper:
> > > /*
> > >  * Compatibility wrapper for older platforms that do not care about
> > >  * passing the parent device.
> > >  */
> > > static inline void pci_common_init(struct hw_pci *hw)
> > > {
> > >         pci_common_init_dev(NULL, hw);
> > > }
> > > 
> > > which means that pci_bus_assign_domain_nr() can be called without
> > > a parent. This patch fixes the NULL pointer dereference.
> > > 
> > > Signed-off-by: Krzysztof Ha??asa <khalasa@piap.pl>
> > > Cc: stable@vger.kernel.org
> > 
> > I applied this to for-linus with changelog as below for v4.5, thanks!
> > 
> > Wow, this is terrible.  All ARM32 systems that use pci_common_init()
> > crash at boot.  That includes cns3xxx, dove, footbridge, iopl13xx,
> > ip32x, iop33x, ixp4xx, ks8695, mv78xx0, orion5x, pxa, sa1100, etc.
> > Apparently they've been crashing since v4.0, when 7c674700098c and
> > 8c7d14746abc appeared.  I can hardly believe nobody noticed until now.
> > 
> > Actually, I did find one problem report:
> > http://forum.doozan.com/read.php?2,17868,22070,quote=1 from last May,
> > but apparently it got lost in a forum and never found its way
> > upstream.
> > 
> > I reworked the changelog because this problem will affect *any* arch
> > that enables CONFIG_PCI_DOMAINS_GENERIC and supplies NULL "parent"
> > pointers -- ia64, mips, mn10300, s390, x86, etc., would be affected if
> > they enabled CONFIG_PCI_DOMAINS_GENERIC.
> > 
> > I also added a "Fixes:" tag for 7c674700098c, since that's the commit
> > that added the generic code we're fixing.  Backports of 7c674700098c
> > should also backport this change.
> 
> That's really unfortunate, when I moved code from arm64 to generic I
> did not spot this issue in the original code and carried it over, you
> summarized the reasons in the commit log so without any further ado (and
> with my apologies):
> 
> Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

No worries, it just goes with the territory.  What surprises me is
that it took us so long to notice.  v4.0 was released almost a year
ago (April 12, 2015), so I can't figure out how nobody noticed until
now.

And I don't know what happened with the problem report in the forum.
That's a case where somebody *did* notice, but I guess they just gave
up on v4.0 and went back to v3.18.  What a shame :)  I don't know if
people just have low expectations of Linux, or they feel like it's too
hard to report bugs, or we don't make it easy enough, or we're not
approachable enough, or what.  I notice that many times somebody finds
a workaround, and people seem satisfied with that, and we don't get a
chance to fix the real problem.

Bjorn

> > commit 71babd2a89fe
> > Author: Krzysztof =?utf-8?Q?Ha=C5=82asa?= <khalasa@piap.pl>
> > Date:   Tue Mar 1 07:07:18 2016 +0100
> > 
> >     PCI: Allow a NULL "parent" pointer in pci_bus_assign_domain_nr()
> >     
> >     pci_create_root_bus() passes a "parent" pointer to
> >     pci_bus_assign_domain_nr().  When CONFIG_PCI_DOMAINS_GENERIC is defined,
> >     pci_bus_assign_domain_nr() dereferences that pointer.  Many callers of
> >     pci_create_root_bus() supply a NULL "parent" pointer, which leads to a NULL
> >     pointer dereference error.
> >     
> >     7c674700098c ("PCI: Move domain assignment from arm64 to generic code")
> >     moved the "parent" dereference from arm64 to generic code.  Only arm64 used
> >     that code (because only arm64 defined CONFIG_PCI_DOMAINS_GENERIC), and it
> >     always supplied a valid "parent" pointer.  Other arches supplied NULL
> >     "parent" pointers but didn't defined CONFIG_PCI_DOMAINS_GENERIC, so they
> >     used a no-op version of pci_bus_assign_domain_nr().
> >     
> >     8c7d14746abc ("ARM/PCI: Move to generic PCI domains") defined
> >     CONFIG_PCI_DOMAINS_GENERIC on ARM, and many ARM platforms use
> >     pci_common_init(), which supplies a NULL "parent" pointer.
> >     These platforms (cns3xxx, dove, footbridge, iop13xx, etc.) crash
> >     with a NULL pointer dereference like this while probing PCI:
> >     
> >       Unable to handle kernel NULL pointer dereference at virtual address 000000a4
> >       PC is at pci_bus_assign_domain_nr+0x10/0x84
> >       LR is at pci_create_root_bus+0x48/0x2e4
> >       Kernel panic - not syncing: Attempted to kill init!
> >     
> >     [bhelgaas: changelog, add "Reported:" and "Fixes:" tags]
> >     Reported: http://forum.doozan.com/read.php?2,17868,22070,quote=1
> >     Fixes: 8c7d14746abc ("ARM/PCI: Move to generic PCI domains")
> >     Fixes: 7c674700098c ("PCI: Move domain assignment from arm64 to generic code")
> >     Signed-off-by: Krzysztof Ha??asa <khalasa@piap.pl>
> >     Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> >     CC: stable@vger.kernel.org	# v4.0+
> > 
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 602eb42..f89db3a 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -4772,8 +4772,10 @@ int pci_get_new_domain_nr(void)
> >  void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
> >  {
> >  	static int use_dt_domains = -1;
> > -	int domain = of_get_pci_domain_nr(parent->of_node);
> > +	int domain = -1;
> >  
> > +	if (parent)
> > +		domain = of_get_pci_domain_nr(parent->of_node);
> >  	/*
> >  	 * Check DT domain and use_dt_domains values.
> >  	 *
> > 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
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> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

[Lorenzo Pieralisi]

On Mon, Mar 07, 2016 at 10:24:27PM -0600, Bjorn Helgaas wrote:

[...]

> > > Actually, I did find one problem report:
> > > http://forum.doozan.com/read.php?2,17868,22070,quote=1 from last May,
> > > but apparently it got lost in a forum and never found its way
> > > upstream.
> > > 
> > > I reworked the changelog because this problem will affect *any* arch
> > > that enables CONFIG_PCI_DOMAINS_GENERIC and supplies NULL "parent"
> > > pointers -- ia64, mips, mn10300, s390, x86, etc., would be affected if
> > > they enabled CONFIG_PCI_DOMAINS_GENERIC.
> > > 
> > > I also added a "Fixes:" tag for 7c674700098c, since that's the commit
> > > that added the generic code we're fixing.  Backports of 7c674700098c
> > > should also backport this change.
> > 
> > That's really unfortunate, when I moved code from arm64 to generic I
> > did not spot this issue in the original code and carried it over, you
> > summarized the reasons in the commit log so without any further ado (and
> > with my apologies):
> > 
> > Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> 
> No worries, it just goes with the territory.  What surprises me is
> that it took us so long to notice.  v4.0 was released almost a year
> ago (April 12, 2015), so I can't figure out how nobody noticed until
> now.
> 
> And I don't know what happened with the problem report in the forum.
> That's a case where somebody *did* notice, but I guess they just gave
> up on v4.0 and went back to v3.18.  What a shame :)  I don't know if
> people just have low expectations of Linux, or they feel like it's too
> hard to report bugs, or we don't make it easy enough, or we're not
> approachable enough, or what.  I notice that many times somebody finds
> a workaround, and people seem satisfied with that, and we don't get a
> chance to fix the real problem.

I agree it is a pity the problem was not reported upstream which would
have solved the issue (that I should have spotted anyway while moving
the code) a long time ago, unfortunately I think it has to do with
how often developers/distros upgrade their kernels on these boards/socs
and how they interact with upstream, which is a discussion worth having.

Thank you !
Lorenzo