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mm: mempolicy: turn vma_set_policy() into vma_dup_policy()

PATCH In review Oleg Nesterov 3 participants 7 messages Jul 10, 2013 – Jul 12, 2013

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Oleg Nesterov

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#0 lore raw

PATCH 1/1 mm: mempolicy: turn vma_set_policy() into vma_dup_policy()

Simple cleanup. Every user of vma_set_policy() does the same work, this looks a bit annoying imho. And the new trivial helper which does mpol_dup() + vma_set_policy() to simplify the callers.

Signed-off-by Oleg Nesterov <[email protected]>
---
 include/linux/mempolicy.h |    9 +++++++--
 kernel/fork.c             |    9 +++------
 mm/mempolicy.c            |   10 ++++++++++
 mm/mmap.c                 |   17 +++++------------
 4 files changed, 25 insertions(+), 20 deletions(-)
include/linux/mempolicy.h +7 -2
index 0d7df39..b2f8977 100644
@@ -91,7 +91,6 @@ static inline struct mempolicy *mpol_dup(struct mempolicy *pol)
 }
 
 #define vma_policy(vma) ((vma)->vm_policy)
-#define vma_set_policy(vma, pol) ((vma)->vm_policy = (pol))
 
 static inline void mpol_get(struct mempolicy *pol)
 {

@@ -126,6 +125,7 @@ struct shared_policy {
 	spinlock_t lock;
 };
 
+int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst);
 void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol);
 int mpol_set_shared_policy(struct shared_policy *info,
 				struct vm_area_struct *vma,

@@ -240,7 +240,12 @@ mpol_shared_policy_lookup(struct shared_policy *sp, unsigned long idx)
 }
 
 #define vma_policy(vma) NULL
-#define vma_set_policy(vma, pol) do {} while(0)
+
+static inline int
+vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
+{
+	return 0;
+}
 
 static inline void numa_policy_init(void)
 {
kernel/fork.c +3 -6
index 987b28a..1c214fe 100644
@@ -351,7 +351,6 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 	struct rb_node **rb_link, *rb_parent;
 	int retval;
 	unsigned long charge;
-	struct mempolicy *pol;
 
 	uprobe_start_dup_mmap();
 	down_write(&oldmm->mmap_sem);

@@ -402,11 +401,9 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 			goto fail_nomem;
 		*tmp = *mpnt;
 		INIT_LIST_HEAD(&tmp->anon_vma_chain);
-		pol = mpol_dup(vma_policy(mpnt));
-		retval = PTR_ERR(pol);
-		if (IS_ERR(pol))
+		retval = vma_dup_policy(mpnt, tmp);
+		if (retval)
 			goto fail_nomem_policy;
-		vma_set_policy(tmp, pol);
 		tmp->vm_mm = mm;
 		if (anon_vma_fork(tmp, mpnt))
 			goto fail_nomem_anon_vma_fork;

@@ -474,7 +471,7 @@ out:
 	uprobe_end_dup_mmap();
 	return retval;
 fail_nomem_anon_vma_fork:
-	mpol_put(pol);
+	mpol_put(vma_policy(tmp));
 fail_nomem_policy:
 	kmem_cache_free(vm_area_cachep, tmp);
 fail_nomem:
mm/mempolicy.c +10 -0
index 4baf12e..6b1d426 100644
@@ -2065,6 +2065,16 @@ retry_cpuset:
 }
 EXPORT_SYMBOL(alloc_pages_current);
 
+int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
+{
+	struct mempolicy *pol = mpol_dup(vma_policy(src));
+
+	if (IS_ERR(pol))
+		return PTR_ERR(pol);
+	dst->vm_policy = pol;
+	return 0;
+}
+
 /*
  * If mpol_dup() sees current->cpuset == cpuset_being_rebound, then it
  * rebinds the mempolicy its copying by calling mpol_rebind_policy()
mm/mmap.c +5 -12
index 7a1ba76..d8a310b 100644
@@ -2481,7 +2481,6 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
 static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
 	      unsigned long addr, int new_below)
 {
-	struct mempolicy *pol;
 	struct vm_area_struct *new;
 	int err = -ENOMEM;
 

@@ -2505,12 +2504,9 @@ static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
 		new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
 	}
 
-	pol = mpol_dup(vma_policy(vma));
-	if (IS_ERR(pol)) {
-		err = PTR_ERR(pol);
+	err = vma_dup_policy(vma, new);
+	if (err)
 		goto out_free_vma;
-	}
-	vma_set_policy(new, pol);
 
 	if (anon_vma_clone(new, vma))
 		goto out_free_mpol;

@@ -2538,7 +2534,7 @@ static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
 		fput(new->vm_file);
 	unlink_anon_vmas(new);
  out_free_mpol:
-	mpol_put(pol);
+	mpol_put(vma_policy(new));
  out_free_vma:
 	kmem_cache_free(vm_area_cachep, new);
  out_err:

@@ -2881,7 +2877,6 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	struct mm_struct *mm = vma->vm_mm;
 	struct vm_area_struct *new_vma, *prev;
 	struct rb_node **rb_link, *rb_parent;
-	struct mempolicy *pol;
 	bool faulted_in_anon_vma = true;
 
 	/*

@@ -2926,10 +2921,8 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 			new_vma->vm_start = addr;
 			new_vma->vm_end = addr + len;
 			new_vma->vm_pgoff = pgoff;
-			pol = mpol_dup(vma_policy(vma));
-			if (IS_ERR(pol))
+			if (vma_dup_policy(vma, new_vma))
 				goto out_free_vma;
-			vma_set_policy(new_vma, pol);
 			INIT_LIST_HEAD(&new_vma->anon_vma_chain);
 			if (anon_vma_clone(new_vma, vma))
 				goto out_free_mempol;

@@ -2944,7 +2937,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	return new_vma;
 
  out_free_mempol:
-	mpol_put(pol);
+	mpol_put(vma_policy(new_vma));
  out_free_vma:
 	kmem_cache_free(vm_area_cachep, new_vma);
 	return NULL;
Signature · 1 line
1.5.5.1
#1 lore raw
Quoted 4 lines · Oleg Nesterov

Simple cleanup. Every user of vma_set_policy() does the same work, this looks a bit annoying imho. And the new trivial helper which does mpol_dup() + vma_set_policy() to simplify the callers.

Good idea, just a few simple issues to fix.

Quoted 5 lines
mm/mempolicy.c +0 -0
index 4baf12e..6b1d426 100644

mm/mempolicy.c retry_cpuset: · line 2073

Quoted 9 lines
mm/mempolicy.c +6 -0
@@ -2065,6 +2065,16 @@ retry_cpuset:
 }
 EXPORT_SYMBOL(alloc_pages_current);
 
+int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
+{
+	struct mempolicy *pol = mpol_dup(vma_policy(src));
+
+	if (IS_ERR(pol))
+		return PTR_ERR(pol);

PTR_ERR() returns long, so vma_dup_policy() needs to return long.

Quoted 24 lines
mm/mempolicy.c +4 -0
+	dst->vm_policy = pol;
+	return 0;
+}
+
 /*
  * If mpol_dup() sees current->cpuset == cpuset_being_rebound, then it
  * rebinds the mempolicy its copying by calling mpol_rebind_policy()
mm/mmap.c +0 -2
index 7a1ba76..d8a310b 100644
@@ -2481,7 +2481,6 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
 static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
 	      unsigned long addr, int new_below)
 {
-	struct mempolicy *pol;
 	struct vm_area_struct *new;
 	int err = -ENOMEM;
 

@@ -2505,12 +2504,9 @@ static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
 		new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
 	}
 
-	pol = mpol_dup(vma_policy(vma));

mm/mmap.c static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma, · line 2512

Quoted 10 lines
mm/mmap.c +2 -4
-	if (IS_ERR(pol)) {
-		err = PTR_ERR(pol);
+	err = vma_dup_policy(vma, new);
+	if (err)
 		goto out_free_vma;
-	}
-	vma_set_policy(new, pol);
 
 	if (anon_vma_clone(new, vma))
 		goto out_free_mpol;

This isn't the first occurrence in mm/mmap.c, what about vma_adjust()? Probably need to patch 3.10 or later.

Otherwise looks good.

maintainer
#2 lore raw
Quoted 8 lines · On Thu, 11 Jul 2013 15:13:03 -0700 (PDT) David Rientjes <[email protected]>…

mm/mempolicy.c retry_cpuset: · line 2073

Quoted 6 lines
mm/mempolicy.c +6 -0
+int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
+{
+	struct mempolicy *pol = mpol_dup(vma_policy(src));
+
+	if (IS_ERR(pol))
+		return PTR_ERR(pol);

PTR_ERR() returns long, so vma_dup_policy() needs to return long.

hm, really? vma_dup_policy() returns an errno and errnos have type "int".

Arguably it is PTR_ERR() which returns the wrong type...

#3 lore raw
Quoted 11 lines · Andrew Morton
Quoted 8 lines · On Thu, 11 Jul 2013 15:13:03 -0700 (PDT) David Rientjes <[email protected]>…

mm/mempolicy.c retry_cpuset: · line 2073

Quoted 6 lines
mm/mempolicy.c +6 -0
+int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
+{
+	struct mempolicy *pol = mpol_dup(vma_policy(src));
+
+	if (IS_ERR(pol))
+		return PTR_ERR(pol);

PTR_ERR() returns long, so vma_dup_policy() needs to return long.

Quoted 4 lines

hm, really? vma_dup_policy() returns an errno and errnos have type "int".

Arguably it is PTR_ERR() which returns the wrong type...

PTR_ERR() may not imply IS_ERR(), which I believe Rusty is trying to fix with his series that fixes up abuses of PTR_ERR(). But I agree that vma_dup_policy() can return int because of the IS_ERR() check as written.

For complete correctness there should probably be a build error if MAX_ERRNO cannot fit in an int and then this should do return (int)PTR_ERR(pol) to make it clear.

maintainer
#4 lore raw
Quoted 13 lines · On Thu, 11 Jul 2013 15:27:46 -0700 (PDT) David Rientjes <[email protected]>…
Quoted 11 lines · Andrew Morton
Quoted 8 lines · On Thu, 11 Jul 2013 15:13:03 -0700 (PDT) David Rientjes <[email protected]>…

mm/mempolicy.c retry_cpuset: · line 2073

Quoted 6 lines
mm/mempolicy.c +6 -0
+int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
+{
+	struct mempolicy *pol = mpol_dup(vma_policy(src));
+
+	if (IS_ERR(pol))
+		return PTR_ERR(pol);

PTR_ERR() returns long, so vma_dup_policy() needs to return long.

Quoted 6 lines
Quoted 4 lines

hm, really? vma_dup_policy() returns an errno and errnos have type "int".

Arguably it is PTR_ERR() which returns the wrong type...

PTR_ERR() may not imply IS_ERR(),

Well why not. Are we saying that code can legitimately convert the PTR_ERR() return value back into a pointer? If so that sounds nuts.

Quoted 2 lines

which I believe Rusty is trying to fix with his series that fixes up abuses of PTR_ERR().

Well I hope all of this will be completely documented in err.h. Otherwise the abuses will simply continue.

#5 lore raw
Quoted 5 lines · Andrew Morton
Quoted 1 line

PTR_ERR() may not imply IS_ERR(),

Well why not. Are we saying that code can legitimately convert the PTR_ERR() return value back into a pointer? If so that sounds nuts.

ERR_PTR() is just delivering a payload that can be interpreted by PTR_ERR(), Rusty has spotted places in the kernel that do this without actual errno. The most obvious case for me is the ERR_PTR(-1UL) in mm/oom_kill.c.

People delivering a non-errno payload shouldn't be using ERR_PTR(), but nothing enforces that. You could add a WARN_ON_ONCE(error >= MAX_ERRNO). But PTR_ERR() will still need to rely on IS_ERR().

I agree that these longs should be converted to ints, since errno is defined to be int by the C standard.

author
#6 lore raw
In reply to David Rientjes
Quoted 11 lines · David Rientjes

Review

Quoted 6 lines · Oleg Nesterov
(quoted diff) +6 -0
+int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
+{
+	struct mempolicy *pol = mpol_dup(vma_policy(src));
+
+	if (IS_ERR(pol))
+		return PTR_ERR(pol);

PTR_ERR() returns long, so vma_dup_policy() needs to return long.

I think that "int" should be fine, or we should fix IS_ERR/ERR_PTR. If nothing else, the changed code did the same. And there are a lot of other "int" functions which return PTR_ERR().

But I agree, this is only correct because vma_dup_policy() checks IS_ERR() before PTR_ERR(), and because mpol_dup() doesn't do the wrong things with ERR_PTR().

For example, ERR_PTR(args->err) in hw_breakpoint_handler() looks really strange and imho should be killed. But correct, it is not actually the error.

Quoted 13 lines
Quoted 13 lines
(quoted diff) +2 -5
@@ -2505,12 +2504,9 @@ static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
 		new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
 	}
 
-	pol = mpol_dup(vma_policy(vma));
-	if (IS_ERR(pol)) {
-		err = PTR_ERR(pol);
+	err = vma_dup_policy(vma, new);
+	if (err)
 		goto out_free_vma;
-	}
-	vma_set_policy(new, pol);
Quoted 5 lines

Review static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma, · line 2512

Quoted 2 lines
(quoted diff) +0 -0
 	if (anon_vma_clone(new, vma))
 		goto out_free_mpol;

This isn't the first occurrence in mm/mmap.c, what about vma_adjust()? Probably need to patch 3.10 or later.

Ah, sorry for confusion, I forgot to mention that this is on top of another -mm patch,

mm-mempolicy-fix-mbind_range-vma_adjust-interaction.patch

attached below just in case.

Quoted 1 line

Otherwise looks good.

Thanks for review ;)

Oleg.

-----------------------------------------------------------------------
[PATCH] mm: mempolicy: fix mbind_range() && vma_adjust() interaction

vma_adjust() does vma_set_policy(vma, vma_policy(next)) and this is doubly wrong:

1. This leaks vma->vm_policy if it is not NULL and not equal to next->vm_policy.

This can happen if vma_merge() expands "area", not prev (case 8).

2. This sets the wrong policy if vma_merge() joins prev and area, area is the vma the caller needs to update and it still has the old policy.

Revert 1444f92c "mm: merging memory blocks resets mempolicy" which introduced these problems.

Change mbind_range() to recheck mpol_equal() after vma_merge() to fix the problem 1444f92c tried to address.

Signed-off-by Oleg Nesterov <[email protected]>
Cc <[email protected]>
---
 mm/mempolicy.c |    6 +++++-
 mm/mmap.c      |    2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)
mm/mempolicy.c +5 -1
index 7431001..4baf12e 100644
@@ -732,7 +732,10 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
 		if (prev) {
 			vma = prev;
 			next = vma->vm_next;
-			continue;
+			if (mpol_equal(vma_policy(vma), new_pol))
+				continue;
+			/* vma_merge() joined vma && vma->next, case 8 */
+			goto replace;
 		}
 		if (vma->vm_start != vmstart) {
 			err = split_vma(vma->vm_mm, vma, vmstart, 1);

@@ -744,6 +747,7 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
 			if (err)
 				goto out;
 		}
+ replace:
 		err = vma_replace_policy(vma, new_pol);
 		if (err)
 			goto out;
mm/mmap.c +1 -1
index 7fe7f0b..42234b8 100644
@@ -865,7 +865,7 @@ again:			remove_next = 1 + (end > next->vm_end);
 		if (next->anon_vma)
 			anon_vma_merge(vma, next);
 		mm->map_count--;
-		vma_set_policy(vma, vma_policy(next));
+		mpol_put(vma_policy(next));
 		kmem_cache_free(vm_area_cachep, next);
 		/*
 		 * In mprotect's case 6 (see comments on vma_merge),
Signature · 1 line
1.5.5.1