[PATCH] powerpc: thp: Fix crash on mremap

[PATCH] powerpc: thp: Fix crash on mremap

[Aneesh Kumar K.V]

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

This patch fix the below crash

NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
LR [c0000000000439ac] .hash_page+0x18c/0x5e0
...
Call Trace:
[c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
[437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
[437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58

On ppc64 we use the pgtable for storing the hpte slot information and
store address to the pgtable at a constant offset (PTRS_PER_PMD) from
pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
from new pmd.

We also want to move the withdraw and deposit before the set_pmd so
that, when page fault find the pmd as trans huge we can be sure that
pgtable can be located at the offset.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
NOTE:
For other archs we would just be removing the pgtable from the list and adding it back.
I didn't find an easy way to make it not do that without lots of #ifdef around. Any
suggestion around that is welcome.

 mm/huge_memory.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7de1bf85f683..eb2e60d9ba45 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1500,24 +1500,23 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
 	 */
 	ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
 	if (ret == 1) {
+		pgtable_t pgtable;
+
 		new_ptl = pmd_lockptr(mm, new_pmd);
 		if (new_ptl != old_ptl)
 			spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
 		VM_BUG_ON(!pmd_none(*new_pmd));
+		/*
+		 * Archs like ppc64 use pgtable to store per pmd
+		 * specific information. So when we switch the pmd,
+		 * we should also withdraw and deposit the pgtable
+		 */
+		pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
+		pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
 		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
-		if (new_ptl != old_ptl) {
-			pgtable_t pgtable;
-
-			/*
-			 * Move preallocated PTE page table if new_pmd is on
-			 * different PMD page table.
-			 */
-			pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
-			pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
-
+		if (new_ptl != old_ptl)
 			spin_unlock(new_ptl);
-		}
 		spin_unlock(old_ptl);
 	}
 out:
-- 
1.8.3.2

Re: [PATCH] powerpc: thp: Fix crash on mremap

[Benjamin Herrenschmidt]

On Wed, 2014-01-01 at 15:23 +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> 
> This patch fix the below crash
> 
> NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
> LR [c0000000000439ac] .hash_page+0x18c/0x5e0
> ...
> Call Trace:
> [c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
> [437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
> [437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58
> 
> On ppc64 we use the pgtable for storing the hpte slot information and
> store address to the pgtable at a constant offset (PTRS_PER_PMD) from
> pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
> the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
> from new pmd.
> 
> We also want to move the withdraw and deposit before the set_pmd so
> that, when page fault find the pmd as trans huge we can be sure that
> pgtable can be located at the offset.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
> NOTE:
> For other archs we would just be removing the pgtable from the list and adding it back.
> I didn't find an easy way to make it not do that without lots of #ifdef around. Any
> suggestion around that is welcome.

What about

-		if (new_ptl != old_ptl) {
+               if (new_ptl != old_ptl || ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW) {

Or something similar ?

Cheers,
Ben.

>  mm/huge_memory.c | 21 ++++++++++-----------
>  1 file changed, 10 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 7de1bf85f683..eb2e60d9ba45 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1500,24 +1500,23 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
>  	 */
>  	ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
>  	if (ret == 1) {
> +		pgtable_t pgtable;
> +
>  		new_ptl = pmd_lockptr(mm, new_pmd);
>  		if (new_ptl != old_ptl)
>  			spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
>  		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
>  		VM_BUG_ON(!pmd_none(*new_pmd));
> +		/*
> +		 * Archs like ppc64 use pgtable to store per pmd
> +		 * specific information. So when we switch the pmd,
> +		 * we should also withdraw and deposit the pgtable
> +		 */
> +		pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
> +		pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
>  		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
> -		if (new_ptl != old_ptl) {
> -			pgtable_t pgtable;
> -
> -			/*
> -			 * Move preallocated PTE page table if new_pmd is on
> -			 * different PMD page table.
> -			 */
> -			pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
> -			pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
> -
> +		if (new_ptl != old_ptl)
>  			spin_unlock(new_ptl);
> -		}
>  		spin_unlock(old_ptl);
>  	}
>  out:

Re: [PATCH] powerpc: thp: Fix crash on mremap

[Kirill A. Shutemov]

On Wed, Jan 01, 2014 at 09:29:05PM +1100, Benjamin Herrenschmidt wrote:
> On Wed, 2014-01-01 at 15:23 +0530, Aneesh Kumar K.V wrote:
> > From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> > 
> > This patch fix the below crash
> > 
> > NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
> > LR [c0000000000439ac] .hash_page+0x18c/0x5e0
> > ...
> > Call Trace:
> > [c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
> > [437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
> > [437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58
> > 
> > On ppc64 we use the pgtable for storing the hpte slot information and
> > store address to the pgtable at a constant offset (PTRS_PER_PMD) from
> > pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
> > the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
> > from new pmd.
> > 
> > We also want to move the withdraw and deposit before the set_pmd so
> > that, when page fault find the pmd as trans huge we can be sure that
> > pgtable can be located at the offset.
> > 
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> > ---
> > NOTE:
> > For other archs we would just be removing the pgtable from the list and adding it back.
> > I didn't find an easy way to make it not do that without lots of #ifdef around. Any
> > suggestion around that is welcome.
> 
> What about
> 
> -		if (new_ptl != old_ptl) {
> +               if (new_ptl != old_ptl || ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW) {
> 
> Or something similar ?

Looks sane to me. Or something with IS_ENABLED(), if needed.

> 
> Cheers,
> Ben.
> 
> >  mm/huge_memory.c | 21 ++++++++++-----------
> >  1 file changed, 10 insertions(+), 11 deletions(-)
> > 
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 7de1bf85f683..eb2e60d9ba45 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1500,24 +1500,23 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
> >  	 */
> >  	ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
> >  	if (ret == 1) {
> > +		pgtable_t pgtable;
> > +
> >  		new_ptl = pmd_lockptr(mm, new_pmd);
> >  		if (new_ptl != old_ptl)
> >  			spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
> >  		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
> >  		VM_BUG_ON(!pmd_none(*new_pmd));
> > +		/*
> > +		 * Archs like ppc64 use pgtable to store per pmd
> > +		 * specific information. So when we switch the pmd,
> > +		 * we should also withdraw and deposit the pgtable
> > +		 */
> > +		pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
> > +		pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
> >  		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
> > -		if (new_ptl != old_ptl) {
> > -			pgtable_t pgtable;
> > -
> > -			/*
> > -			 * Move preallocated PTE page table if new_pmd is on
> > -			 * different PMD page table.
> > -			 */

Please don't lose the comment.

> > -			pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
> > -			pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
> > -
> > +		if (new_ptl != old_ptl)
> >  			spin_unlock(new_ptl);
> > -		}
> >  		spin_unlock(old_ptl);
> >  	}
> >  out:
> 
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

-- 
 Kirill A. Shutemov

Re: [PATCH] powerpc: thp: Fix crash on mremap

[Andrew Morton]

On Thu, 2 Jan 2014 04:19:51 +0200 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:

> On Wed, Jan 01, 2014 at 09:29:05PM +1100, Benjamin Herrenschmidt wrote:
> > On Wed, 2014-01-01 at 15:23 +0530, Aneesh Kumar K.V wrote:
> > > From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> > > 
> > > This patch fix the below crash
> > > 
> > > NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
> > > LR [c0000000000439ac] .hash_page+0x18c/0x5e0
> > > ...
> > > Call Trace:
> > > [c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
> > > [437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
> > > [437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58
> > > 
> > > On ppc64 we use the pgtable for storing the hpte slot information and
> > > store address to the pgtable at a constant offset (PTRS_PER_PMD) from
> > > pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
> > > the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
> > > from new pmd.
> > > 
> > > We also want to move the withdraw and deposit before the set_pmd so
> > > that, when page fault find the pmd as trans huge we can be sure that
> > > pgtable can be located at the offset.
> > > 

Did this get fixed?

Re: [PATCH] powerpc: thp: Fix crash on mremap

[Kirill A. Shutemov]

On Mon, Jan 13, 2014 at 02:17:48PM -0800, Andrew Morton wrote:
> On Thu, 2 Jan 2014 04:19:51 +0200 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:
> 
> > On Wed, Jan 01, 2014 at 09:29:05PM +1100, Benjamin Herrenschmidt wrote:
> > > On Wed, 2014-01-01 at 15:23 +0530, Aneesh Kumar K.V wrote:
> > > > From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> > > > 
> > > > This patch fix the below crash
> > > > 
> > > > NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
> > > > LR [c0000000000439ac] .hash_page+0x18c/0x5e0
> > > > ...
> > > > Call Trace:
> > > > [c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
> > > > [437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
> > > > [437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58
> > > > 
> > > > On ppc64 we use the pgtable for storing the hpte slot information and
> > > > store address to the pgtable at a constant offset (PTRS_PER_PMD) from
> > > > pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
> > > > the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
> > > > from new pmd.
> > > > 
> > > > We also want to move the withdraw and deposit before the set_pmd so
> > > > that, when page fault find the pmd as trans huge we can be sure that
> > > > pgtable can be located at the offset.
> > > > 
> 
> Did this get fixed?

New version: http://thread.gmane.org/gmane.linux.kernel.mm/111809

-- 
 Kirill A. Shutemov

Re: [PATCH] powerpc: thp: Fix crash on mremap

[Benjamin Herrenschmidt]

On Mon, 2014-01-13 at 14:17 -0800, Andrew Morton wrote:

> Did this get fixed?

Any chance you can Ack the patch on that thread ?

http://thread.gmane.org/gmane.linux.kernel.mm/111809

So I can put it in powerpc -next with a CC stable ? Or if you tell me
tat Kirill Ack is sufficient then I'll go for it.

Cheers,
Ben.

Re: [PATCH] powerpc: thp: Fix crash on mremap

[Andrew Morton]

On Tue, 14 Jan 2014 15:13:30 +1100 Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> On Mon, 2014-01-13 at 14:17 -0800, Andrew Morton wrote:
> 
> > Did this get fixed?
> 
> Any chance you can Ack the patch on that thread ?
> 
> http://thread.gmane.org/gmane.linux.kernel.mm/111809
> 
> So I can put it in powerpc -next with a CC stable ? Or if you tell me
> tat Kirill Ack is sufficient then I'll go for it.

yup, it looks OK to me from a non-ppc perspective.  Please proceed as
described.

[PATCH] powerpc: thp: Fix crash on mremap

[Aneesh Kumar K.V]

This patch fix the below crash

NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
LR [c0000000000439ac] .hash_page+0x18c/0x5e0
...
Call Trace:
[c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
[437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
[437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58

On ppc64 we use the pgtable for storing the hpte slot information and
store address to the pgtable at a constant offset (PTRS_PER_PMD) from
pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
from new pmd.

We also want to move the withdraw and deposit before the set_pmd so
that, when page fault find the pmd as trans huge we can be sure that
pgtable can be located at the offset.

variant of upstream SHA1: b3084f4db3aeb991c507ca774337c7e7893ed04f
for 3.11 stable series

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/Kconfig                           |  3 +++
 arch/powerpc/platforms/Kconfig.cputype |  1 +
 mm/huge_memory.c                       | 12 ++++++++++++
 3 files changed, 16 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index 1feb169274fe..c5863b35d054 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -368,6 +368,9 @@ config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 config HAVE_ARCH_SOFT_DIRTY
 	bool
 
+config ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
+	bool
+
 config HAVE_MOD_ARCH_SPECIFIC
 	bool
 	help
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 47d9a03dd415..d11a34be018d 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -71,6 +71,7 @@ config PPC_BOOK3S_64
 	select PPC_FPU
 	select PPC_HAVE_PMU_SUPPORT
 	select SYS_SUPPORTS_HUGETLBFS
+	select ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if PPC_64K_PAGES
 
 config PPC_BOOK3E_64
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 12acb0ba7991..beaa7cc9de75 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1461,8 +1461,20 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
 
 	ret = __pmd_trans_huge_lock(old_pmd, vma);
 	if (ret == 1) {
+#ifdef CONFIG_ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
+		pgtable_t pgtable;
+#endif
 		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
 		VM_BUG_ON(!pmd_none(*new_pmd));
+#ifdef CONFIG_ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
+		/*
+		 * Archs like ppc64 use pgtable to store per pmd
+		 * specific information. So when we switch the pmd,
+		 * we should also withdraw and deposit the pgtable
+		 */
+		pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
+		pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
+#endif
 		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
 		spin_unlock(&mm->page_table_lock);
 	}
-- 
1.8.5.3

[PATCH] powerpc: thp: Fix crash on mremap

[Aneesh Kumar K.V]

This patch fix the below crash

NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
LR [c0000000000439ac] .hash_page+0x18c/0x5e0
...
Call Trace:
[c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
[437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
[437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58

On ppc64 we use the pgtable for storing the hpte slot information and
store address to the pgtable at a constant offset (PTRS_PER_PMD) from
pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
from new pmd.

We also want to move the withdraw and deposit before the set_pmd so
that, when page fault find the pmd as trans huge we can be sure that
pgtable can be located at the offset.

variant of upstream SHA1: b3084f4db3aeb991c507ca774337c7e7893ed04f
for 3.12 stable series

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/Kconfig                           |  3 +++
 arch/powerpc/platforms/Kconfig.cputype |  1 +
 mm/huge_memory.c                       | 12 ++++++++++++
 3 files changed, 16 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index af2cc6eabcc7..bca9e7a18bd2 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -365,6 +365,9 @@ config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 config HAVE_ARCH_SOFT_DIRTY
 	bool
 
+config ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
+	bool
+
 config HAVE_MOD_ARCH_SPECIFIC
 	bool
 	help
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 6704e2e20e6b..0225011231ea 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -71,6 +71,7 @@ config PPC_BOOK3S_64
 	select PPC_FPU
 	select PPC_HAVE_PMU_SUPPORT
 	select SYS_SUPPORTS_HUGETLBFS
+	select ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if PPC_64K_PAGES
 
 config PPC_BOOK3E_64
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 292a266e0d42..89b7a647f1cb 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1474,8 +1474,20 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
 
 	ret = __pmd_trans_huge_lock(old_pmd, vma);
 	if (ret == 1) {
+#ifdef CONFIG_ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
+		pgtable_t pgtable;
+#endif
 		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
 		VM_BUG_ON(!pmd_none(*new_pmd));
+#ifdef CONFIG_ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
+		/*
+		 * Archs like ppc64 use pgtable to store per pmd
+		 * specific information. So when we switch the pmd,
+		 * we should also withdraw and deposit the pgtable
+		 */
+		pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
+		pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
+#endif
 		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
 		spin_unlock(&mm->page_table_lock);
 	}
-- 
1.8.5.3

Re: [PATCH] powerpc: thp: Fix crash on mremap

[Luis Henriques]

On Tue, Jan 28, 2014 at 05:47:03PM +0530, Aneesh Kumar K.V wrote:
> This patch fix the below crash
> 
> NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
> LR [c0000000000439ac] .hash_page+0x18c/0x5e0
> ...
> Call Trace:
> [c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
> [437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
> [437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58
> 
> On ppc64 we use the pgtable for storing the hpte slot information and
> store address to the pgtable at a constant offset (PTRS_PER_PMD) from
> pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
> the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
> from new pmd.
> 
> We also want to move the withdraw and deposit before the set_pmd so
> that, when page fault find the pmd as trans huge we can be sure that
> pgtable can be located at the offset.
> 
> variant of upstream SHA1: b3084f4db3aeb991c507ca774337c7e7893ed04f
> for 3.11 stable series
> 

Since both you and Benjamin Herrenschmidt claim this is good for stable, I
am queuing this variant for the 3.11 kernel.  Thanks a lot!

Cheers,
--
Luis

> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
>  arch/Kconfig                           |  3 +++
>  arch/powerpc/platforms/Kconfig.cputype |  1 +
>  mm/huge_memory.c                       | 12 ++++++++++++
>  3 files changed, 16 insertions(+)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 1feb169274fe..c5863b35d054 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -368,6 +368,9 @@ config HAVE_ARCH_TRANSPARENT_HUGEPAGE
>  config HAVE_ARCH_SOFT_DIRTY
>  	bool
>  
> +config ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
> +	bool
> +
>  config HAVE_MOD_ARCH_SPECIFIC
>  	bool
>  	help
> diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
> index 47d9a03dd415..d11a34be018d 100644
> --- a/arch/powerpc/platforms/Kconfig.cputype
> +++ b/arch/powerpc/platforms/Kconfig.cputype
> @@ -71,6 +71,7 @@ config PPC_BOOK3S_64
>  	select PPC_FPU
>  	select PPC_HAVE_PMU_SUPPORT
>  	select SYS_SUPPORTS_HUGETLBFS
> +	select ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
>  	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if PPC_64K_PAGES
>  
>  config PPC_BOOK3E_64
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 12acb0ba7991..beaa7cc9de75 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1461,8 +1461,20 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
>  
>  	ret = __pmd_trans_huge_lock(old_pmd, vma);
>  	if (ret == 1) {
> +#ifdef CONFIG_ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
> +		pgtable_t pgtable;
> +#endif
>  		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
>  		VM_BUG_ON(!pmd_none(*new_pmd));
> +#ifdef CONFIG_ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
> +		/*
> +		 * Archs like ppc64 use pgtable to store per pmd
> +		 * specific information. So when we switch the pmd,
> +		 * we should also withdraw and deposit the pgtable
> +		 */
> +		pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
> +		pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
> +#endif
>  		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
>  		spin_unlock(&mm->page_table_lock);
>  	}
> -- 
> 1.8.5.3
> 
> --
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