[PATCH v2] mm: make expand_downwards symmetrical to expand_upwards

[Michal Hocko <mhocko@suse.cz>]

On Sun 17-04-11 20:00:17, Hugh Dickins wrote:
> On Fri, 14 Apr 2011, Michal Hocko wrote:
[...]
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 692dbae..765cf4e 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1498,8 +1498,10 @@ unsigned long ra_submit(struct file_ra_state *ra,
> >  extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
> >  #if VM_GROWSUP
> >  extern int expand_upwards(struct vm_area_struct *vma, unsigned long address);
> > +  #define expand_downwards(vma, address) do { } while (0)
> 
> I think this is wrong: doesn't the VM_GROWSUP case actually want
> a real expand_downwards() in addition to expand_upwards()?

Ahh, right you are. I haven't noticed that we have
expand_stack_downwards as well and this one is called from get_arg_page
if CONFIG_STACK_GROWSUP. 

I am wondering why we do this just for CONFIG_STACK_GROWSUP. Do we
expand stack for GROWSDOWN automatically?

> 
> >  #else
> >    #define expand_upwards(vma, address) do { } while (0)
> > +extern int expand_downwards(struct vm_area_struct *vma, unsigned long address);
> >  #endif
> >  extern int expand_stack_downwards(struct vm_area_struct *vma,
> >  				  unsigned long address);
> 
> And if you're going for symmetry, wouldn't it be nice to add fs/exec.c
> to the patch and remove this silly expand_stack_downwards() wrapper?

Sounds reasonable. Thanks for the review, Hugh. I am also thinking
whether expand_stack_{downwards,upwards} is more suitable name for those
functions as we are more explicit that this is stack related.

What about the updated patch bellow?

Changes since v1
 - fixed expand_downwards case for CONFIG_STACK_GROWSUP in get_arg_page.
 - rename expand_{downwards,upwards} -> expand_stack_{downwards,upwards}
---

>From f3adcf40518eaf7c4ee1cb10abd16b59785a66ba Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.cz>
Date: Fri, 15 Apr 2011 14:56:26 +0200
Subject: [PATCH] mm: make expand_downwards symmetrical to expand_upwards

Currently we have expand_upwards exported while expand_downwards is
accessible only via expand_stack or expand_stack_downwards.

check_stack_guard_page is a nice example of the asymmetry. It uses
expand_stack for VM_GROWSDOWN while expand_upwards is called for
VM_GROWSUP case.

Let's clean this up by exporting both functions and make those name
consistent. Let's use expand_stack_{upwards,downwards} so that we are
explicit about stack manipulation in the name. expand_stack_downwards
has to be defined for both CONFIG_STACK_GROWS{UP,DOWN} because
get_arg_page calls the downwards version in the early process
initialization phase for growsup configuration.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
---
 include/linux/mm.h |   13 ++++++++-----
 mm/memory.c        |    4 ++--
 mm/mmap.c          |   13 ++++---------
 3 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 692dbae..17f9b86 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1494,15 +1494,18 @@ unsigned long ra_submit(struct file_ra_state *ra,
 			struct address_space *mapping,
 			struct file *filp);
 
-/* Do stack extension */
+/* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */
 extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
+
+/* CONFIG_STACK_GROWSUP still needs to to grow downwards at some places */
+extern int expand_stack_downwards(struct vm_area_struct *vma,
+		unsigned long address);
 #if VM_GROWSUP
-extern int expand_upwards(struct vm_area_struct *vma, unsigned long address);
+extern int expand_stack_upwards(struct vm_area_struct *vma,
+		unsigned long address);
 #else
-  #define expand_upwards(vma, address) do { } while (0)
+  #define expand_stack_upwards(vma, address) do { } while (0)
 #endif
-extern int expand_stack_downwards(struct vm_area_struct *vma,
-				  unsigned long address);
 
 /* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
 extern struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long addr);
diff --git a/mm/memory.c b/mm/memory.c
index ce22a25..ba5b4d8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2969,7 +2969,7 @@ static inline int check_stack_guard_page(struct vm_area_struct *vma, unsigned lo
 		if (prev && prev->vm_end == address)
 			return prev->vm_flags & VM_GROWSDOWN ? 0 : -ENOMEM;
 
-		expand_stack(vma, address - PAGE_SIZE);
+		expand_stack_downwards(vma, address - PAGE_SIZE);
 	}
 	if ((vma->vm_flags & VM_GROWSUP) && address + PAGE_SIZE == vma->vm_end) {
 		struct vm_area_struct *next = vma->vm_next;
@@ -2978,7 +2978,7 @@ static inline int check_stack_guard_page(struct vm_area_struct *vma, unsigned lo
 		if (next && next->vm_start == address + PAGE_SIZE)
 			return next->vm_flags & VM_GROWSUP ? 0 : -ENOMEM;
 
-		expand_upwards(vma, address + PAGE_SIZE);
+		expand_stack_upwards(vma, address + PAGE_SIZE);
 	}
 	return 0;
 }
diff --git a/mm/mmap.c b/mm/mmap.c
index e27e0cf..29c68b0 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1731,7 +1731,7 @@ static int acct_stack_growth(struct vm_area_struct *vma, unsigned long size, uns
  * PA-RISC uses this for its stack; IA64 for its Register Backing Store.
  * vma is the last one with address > vma->vm_end.  Have to extend vma.
  */
-int expand_upwards(struct vm_area_struct *vma, unsigned long address)
+int expand_stack_upwards(struct vm_area_struct *vma, unsigned long address)
 {
 	int error;
 
@@ -1782,7 +1782,7 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
 /*
  * vma is the first one with address < vma->vm_start.  Have to extend vma.
  */
-static int expand_downwards(struct vm_area_struct *vma,
+int expand_stack_downwards(struct vm_area_struct *vma,
 				   unsigned long address)
 {
 	int error;
@@ -1829,15 +1829,10 @@ static int expand_downwards(struct vm_area_struct *vma,
 	return error;
 }
 
-int expand_stack_downwards(struct vm_area_struct *vma, unsigned long address)
-{
-	return expand_downwards(vma, address);
-}
-
 #ifdef CONFIG_STACK_GROWSUP
 int expand_stack(struct vm_area_struct *vma, unsigned long address)
 {
-	return expand_upwards(vma, address);
+	return expand_stack_upwards(vma, address);
 }
 
 struct vm_area_struct *
@@ -1859,7 +1854,7 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
 #else
 int expand_stack(struct vm_area_struct *vma, unsigned long address)
 {
-	return expand_downwards(vma, address);
+	return expand_stack_downwards(vma, address);
 }
 
 struct vm_area_struct *
-- 
1.7.4.1

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic