[PATCH] powerpc: mm: fixup preempt undefflow with huge pages

[PATCH] powerpc: mm: fixup preempt undefflow with huge pages

[Sebastian Andrzej Siewior]

hugepd_free() used __get_cpu_var() once. Nothing ensured that the code
accessing the variable did not migrate from one CPU to another and soon
this was noticed by Tiejun Chen in 94b09d755462 ("powerpc/hugetlb:
Replace __get_cpu_var with get_cpu_var"). So we had it fixed.

Christoph Lameter was doing his __get_cpu_var() replaces and forgot
PowerPC. Then he noticed this and sent his fixed up batch again which
got applied as 69111bac42f5 ("powerpc: Replace __get_cpu_var uses").

The careful reader will noticed one little detail: get_cpu_var() got
replaced with this_cpu_ptr(). So now we have a put_cpu_var() which does
a preempt_enable() and nothing that does preempt_disable() so we
underflow the preempt counter.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Tiejun Chen <tiejun.chen@windriver.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/powerpc/mm/hugetlbpage.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 744e24bcb85c..9e8919b39640 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -414,7 +414,7 @@ static void hugepd_free(struct mmu_gather *tlb, void *hugepte)
 {
 	struct hugepd_freelist **batchp;
 
-	batchp = this_cpu_ptr(&hugepd_freelist_cur);
+	batchp = get_cpu_ptr(&hugepd_freelist_cur);
 
 	if (atomic_read(&tlb->mm->mm_users) < 2 ||
 	    cpumask_equal(mm_cpumask(tlb->mm),
-- 
2.7.0

Re: [PATCH] powerpc: mm: fixup preempt undefflow with huge pages

[Aneesh Kumar K.V]

Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:

> [ text/plain ]
> hugepd_free() used __get_cpu_var() once. Nothing ensured that the code
> accessing the variable did not migrate from one CPU to another and soon
> this was noticed by Tiejun Chen in 94b09d755462 ("powerpc/hugetlb:
> Replace __get_cpu_var with get_cpu_var"). So we had it fixed.
>
> Christoph Lameter was doing his __get_cpu_var() replaces and forgot
> PowerPC. Then he noticed this and sent his fixed up batch again which
> got applied as 69111bac42f5 ("powerpc: Replace __get_cpu_var uses").
>
> The careful reader will noticed one little detail: get_cpu_var() got
> replaced with this_cpu_ptr(). So now we have a put_cpu_var() which does
> a preempt_enable() and nothing that does preempt_disable() so we
> underflow the preempt counter.
>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Tiejun Chen <tiejun.chen@windriver.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  arch/powerpc/mm/hugetlbpage.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
> index 744e24bcb85c..9e8919b39640 100644
> --- a/arch/powerpc/mm/hugetlbpage.c
> +++ b/arch/powerpc/mm/hugetlbpage.c
> @@ -414,7 +414,7 @@ static void hugepd_free(struct mmu_gather *tlb, void *hugepte)
>  {
>  	struct hugepd_freelist **batchp;
>
> -	batchp = this_cpu_ptr(&hugepd_freelist_cur);
> +	batchp = get_cpu_ptr(&hugepd_freelist_cur);
>
>  	if (atomic_read(&tlb->mm->mm_users) < 2 ||
>  	    cpumask_equal(mm_cpumask(tlb->mm),

IMHO it would better if we do

batchp = get_cpu_var(hugepd_freelist_cpu);

so that it match the existing

put_cpu_var(hugepd_freelist_cur);

While you are there, can you also fix the wrong indentation on line 423
?

-aneesh

Re: [PATCH] powerpc: mm: fixup preempt undefflow with huge pages

[Benjamin Herrenschmidt]

On Mon, 2016-03-07 at 21:04 +0530, Aneesh Kumar K.V wrote:
> Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:
> 
> While you are there, can you also fix the wrong indentation on line
> 423
> ?

 .../...

Also this looks like stable material no ?

Cheers,
Ben.

Re: [PATCH] powerpc: mm: fixup preempt undefflow with huge pages

[Sebastian Andrzej Siewior]

On 03/08/2016 12:41 AM, Benjamin Herrenschmidt wrote:
> On Mon, 2016-03-07 at 21:04 +0530, Aneesh Kumar K.V wrote:
>> Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:
>>  
>> While you are there, can you also fix the wrong indentation on line
>> 423
>> ?
> 
>  .../...
> 
> Also this looks like stable material no ?

Yes, I had a stable tag attached. I am going to resend it with the
additional changes Aneesh asked for.

> Cheers,
> Ben.
> 
Sebastian

[PATCH v2] powerpc: mm: fixup preempt undefflow with huge pages

[Sebastian Andrzej Siewior]

hugepd_free() used __get_cpu_var() once. Nothing ensured that the code
accessing the variable did not migrate from one CPU to another and soon
this was noticed by Tiejun Chen in 94b09d755462 ("powerpc/hugetlb:
Replace __get_cpu_var with get_cpu_var"). So we had it fixed.

Christoph Lameter was doing his __get_cpu_var() replaces and forgot
PowerPC. Then he noticed this and sent his fixed up batch again which
got applied as 69111bac42f5 ("powerpc: Replace __get_cpu_var uses").

The careful reader will noticed one little detail: get_cpu_var() got
replaced with this_cpu_ptr(). So now we have a put_cpu_var() which does
a preempt_enable() and nothing that does preempt_disable() so we
underflow the preempt counter.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: <stable@vger.kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
v1=E2=80=A6v2: - use get_cpu_var() instead of get_cpu_ptr()
       - correct indentation of put_cpu_var()

 arch/powerpc/mm/hugetlbpage.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 744e24bcb85c..4a811ca7ac9d 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -414,13 +414,13 @@ static void hugepd_free(struct mmu_gather *tlb, void =
*hugepte)
 {
 	struct hugepd_freelist **batchp;
=20
-	batchp =3D this_cpu_ptr(&hugepd_freelist_cur);
+	batchp =3D &get_cpu_var(hugepd_freelist_cur);
=20
 	if (atomic_read(&tlb->mm->mm_users) < 2 ||
 	    cpumask_equal(mm_cpumask(tlb->mm),
 			  cpumask_of(smp_processor_id()))) {
 		kmem_cache_free(hugepte_cache, hugepte);
-        put_cpu_var(hugepd_freelist_cur);
+		put_cpu_var(hugepd_freelist_cur);
 		return;
 	}
=20
--=20
2.7.0

Re: [PATCH v2] powerpc: mm: fixup preempt undefflow with huge pages

[Aneesh Kumar K.V]

Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:

> [ text/plain ]
> hugepd_free() used __get_cpu_var() once. Nothing ensured that the code
> accessing the variable did not migrate from one CPU to another and soon
> this was noticed by Tiejun Chen in 94b09d755462 ("powerpc/hugetlb:
> Replace __get_cpu_var with get_cpu_var"). So we had it fixed.
>
> Christoph Lameter was doing his __get_cpu_var() replaces and forgot
> PowerPC. Then he noticed this and sent his fixed up batch again which
> got applied as 69111bac42f5 ("powerpc: Replace __get_cpu_var uses").
>
> The careful reader will noticed one little detail: get_cpu_var() got
> replaced with this_cpu_ptr(). So now we have a put_cpu_var() which does
> a preempt_enable() and nothing that does preempt_disable() so we
> underflow the preempt counter.
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> v1=E2=80=A6v2: - use get_cpu_var() instead of get_cpu_ptr()
>        - correct indentation of put_cpu_var()
>
>  arch/powerpc/mm/hugetlbpage.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
> index 744e24bcb85c..4a811ca7ac9d 100644
> --- a/arch/powerpc/mm/hugetlbpage.c
> +++ b/arch/powerpc/mm/hugetlbpage.c
> @@ -414,13 +414,13 @@ static void hugepd_free(struct mmu_gather *tlb, voi=
d *hugepte)
>  {
>  	struct hugepd_freelist **batchp;
>=20=20
> -	batchp =3D this_cpu_ptr(&hugepd_freelist_cur);
> +	batchp =3D &get_cpu_var(hugepd_freelist_cur);
>=20=20
>  	if (atomic_read(&tlb->mm->mm_users) < 2 ||
>  	    cpumask_equal(mm_cpumask(tlb->mm),
>  			  cpumask_of(smp_processor_id()))) {
>  		kmem_cache_free(hugepte_cache, hugepte);
> -        put_cpu_var(hugepd_freelist_cur);
> +		put_cpu_var(hugepd_freelist_cur);
>  		return;
>  	}
>=20=20
> --=20
> 2.7.0

Re: [PATCH v2] powerpc: mm: fixup preempt undefflow with huge pages

[Sebastian Andrzej Siewior]

On 2016-03-10 01:04:24 [+0530], Aneesh Kumar K.V wrote:
> Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:

*ping*
http://patchwork.ozlabs.org/patch/593943/

> > [ text/plain ]
> > hugepd_free() used __get_cpu_var() once. Nothing ensured that the code
> > accessing the variable did not migrate from one CPU to another and soon
> > this was noticed by Tiejun Chen in 94b09d755462 ("powerpc/hugetlb:
> > Replace __get_cpu_var with get_cpu_var"). So we had it fixed.
> >
> > Christoph Lameter was doing his __get_cpu_var() replaces and forgot
> > PowerPC. Then he noticed this and sent his fixed up batch again which
> > got applied as 69111bac42f5 ("powerpc: Replace __get_cpu_var uses").
> >
> > The careful reader will noticed one little detail: get_cpu_var() got
> > replaced with this_cpu_ptr(). So now we have a put_cpu_var() which does
> > a preempt_enable() and nothing that does preempt_disable() so we
> > underflow the preempt counter.
> >
>=20
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>=20
> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Cc: Christoph Lameter <cl@linux.com>
> > Cc: Michael Ellerman <mpe@ellerman.id.au>
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > ---
> > v1=E2=80=A6v2: - use get_cpu_var() instead of get_cpu_ptr()
> >        - correct indentation of put_cpu_var()
> >
> >  arch/powerpc/mm/hugetlbpage.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpag=
e.c
> > index 744e24bcb85c..4a811ca7ac9d 100644
> > --- a/arch/powerpc/mm/hugetlbpage.c
> > +++ b/arch/powerpc/mm/hugetlbpage.c
> > @@ -414,13 +414,13 @@ static void hugepd_free(struct mmu_gather *tlb, v=
oid *hugepte)
> >  {
> >  	struct hugepd_freelist **batchp;
> > =20
> > -	batchp =3D this_cpu_ptr(&hugepd_freelist_cur);
> > +	batchp =3D &get_cpu_var(hugepd_freelist_cur);
> > =20
> >  	if (atomic_read(&tlb->mm->mm_users) < 2 ||
> >  	    cpumask_equal(mm_cpumask(tlb->mm),
> >  			  cpumask_of(smp_processor_id()))) {
> >  		kmem_cache_free(hugepte_cache, hugepte);
> > -        put_cpu_var(hugepd_freelist_cur);
> > +		put_cpu_var(hugepd_freelist_cur);
> >  		return;
> >  	}
> > =20

Sebastian

Re: [PATCH v2] powerpc: mm: fixup preempt undefflow with huge pages

[Michael Ellerman]

On Tue, 2016-03-29 at 15:40 +0200, Sebastian Andrzej Siewior wrote:

> On 2016-03-10 01:04:24 [+0530], Aneesh Kumar K.V wrote:

> > Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:
> 
> *ping*
> http://patchwork.ozlabs.org/patch/593943/

*pong*

The merge window just closed, I'm still recovering.

I've got it in my fixes branch locally, I'll probably push that today to
linux-next.

cheers

Re: [PATCH v2] powerpc: mm: fixup preempt undefflow with huge pages

[Sebastian Andrzej Siewior]

On 03/30/2016 02:41 AM, Michael Ellerman wrote:
> The merge window just closed, I'm still recovering.
> 
> I've got it in my fixes branch locally, I'll probably push that today to
> linux-next.

Thank you.

> 
> cheers
> 
Sebastian

Re: [v2] powerpc: mm: fixup preempt undefflow with huge pages

[Michael Ellerman]

On Tue, 2016-08-03 at 09:03:56 UTC, Sebastian Siewior wrote:
> hugepd_free() used __get_cpu_var() once. Nothing ensured that the code
> accessing the variable did not migrate from one CPU to another and soon
> this was noticed by Tiejun Chen in 94b09d755462 ("powerpc/hugetlb:
> Replace __get_cpu_var with get_cpu_var"). So we had it fixed.
> 
> Christoph Lameter was doing his __get_cpu_var() replaces and forgot
> PowerPC. Then he noticed this and sent his fixed up batch again which
> got applied as 69111bac42f5 ("powerpc: Replace __get_cpu_var uses").
> 
> The careful reader will noticed one little detail: get_cpu_var() got
> replaced with this_cpu_ptr(). So now we have a put_cpu_var() which does
> a preempt_enable() and nothing that does preempt_disable() so we
> underflow the preempt counter.
> 
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/08a5bb2921e490939f78f38fd0

cheers