mbind() is required to report EFAULT if range, specified by addr and len,
contains unmapped holes. In current implementation, below rules are applied
for this checking:
1 Unmapped holes at any part of the specified range should be reported as
EFAULT if mbind() for none MPOL_DEFAULT cases;
2 Unmapped holes at any part of the specified range should be ignored (do
not reprot EFAULT) if mbind() for MPOL_DEFAULT case;
3 The whole range in an unmapped hole should be reported as EFAULT;
Note that rule 2 does not fullfill the mbind() API definition, but since
that behavior has existed for long days (the internal flag
MPOL_MF_DISCONTIG_OK is for this purpose), this patch does not plan to
change it.
In current code, application observed inconsistent behavior on rule 1 and
rule 2 respectively. That inconsistency is fixed as below details.
Cases of rule 1:
1) Hole at head side of range. Current code reprot EFAULT, no change by
this patch.
[ vma ][ hole ][ vma ]
[ range ]
2) Hole at middle of range. Current code report EFAULT, no change by
this patch.
[ vma ][ hole ][ vma ]
[ range ]
3) Hole at tail side of range. Current code do not report EFAULT, this
patch fix it.
[ vma ][ hole ][ vma ]
[ range ]
Cases of rule 2:
1) Hole at head side of range. Current code reprot EFAULT, this patch
fix it.
[ vma ][ hole ][ vma ]
[ range ]
2) Hole at middle of range. Current code do not report EFAULT, no change
by this patch.
this patch.
[ vma ][ hole ][ vma]
[ range ]
3) Hole at tail side of range. Current code do not report EFAULT, no
change by this patch.
[ vma ][ hole ][ vma]
[ range ]
This patch has no changes to rule 3.
The unmapped hole checking can also be handled by using .pte_hole(),
instead of .test_walk(). But .pte_hole() is called for holes inside and
outside vma, which causes more cost, so this patch keeps the original
design with .test_walk().
Fixes: 6f4576e3687b ("mempolicy: apply page table walker on queue_pages_range()")
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: linux-man <linux-man@xxxxxxxxxxxxxxx>
Signed-off-by: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
---
send again for removing space
mm/mempolicy.c | 40 +++++++++++++++++++++++++++-------------
1 file changed, 27 insertions(+), 13 deletions(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 807f06f..c697b29 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -410,7 +410,9 @@ struct queue_pages {
struct list_head *pagelist;
unsigned long flags;
nodemask_t *nmask;
- struct vm_area_struct *prev;
+ unsigned long start;
+ unsigned long end;
+ struct vm_area_struct *first;
};
/*
@@ -619,14 +621,20 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
unsigned long flags = qp->flags;
/* range check first */
- if (!(flags & MPOL_MF_DISCONTIG_OK)) {
- if (!vma->vm_next && vma->vm_end < end)
- return -EFAULT;
- if (qp->prev && qp->prev->vm_end < vma->vm_start)
+ VM_BUG_ON((vma->vm_start > start) || (vma->vm_end < end));
+
+ if (!qp->first) {
+ qp->first = vma;
+ if (!(flags & MPOL_MF_DISCONTIG_OK) &&
+ (qp->start < vma->vm_start))
+ /* hole at head side of range */
return -EFAULT;
}
-
- qp->prev = vma;
+ if (!(flags & MPOL_MF_DISCONTIG_OK) &&
+ ((vma->vm_end < qp->end) &&
+ (!vma->vm_next || vma->vm_end < vma->vm_next->vm_start)))
+ /* hole at middle or tail of range */
+ return -EFAULT;
/*
* Need check MPOL_MF_STRICT to return -EIO if possible
@@ -638,8 +646,6 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
if (endvma > end)
endvma = end;
- if (vma->vm_start > start)
- start = vma->vm_start;
if (flags & MPOL_MF_LAZY) {
/* Similar to task_numa_work, skip inaccessible VMAs */
@@ -680,14 +686,23 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
nodemask_t *nodes, unsigned long flags,
struct list_head *pagelist)
{
+ int err;
struct queue_pages qp = {
.pagelist = pagelist,
.flags = flags,
.nmask = nodes,
- .prev = NULL,
+ .start = start,
+ .end = end,
+ .first = NULL,
};
- return walk_page_range(mm, start, end, &queue_pages_walk_ops, &qp);
+ err = walk_page_range(mm, start, end, &queue_pages_walk_ops, &qp);
+
+ if (!qp.first)
+ /* whole range in hole */
+ err = -EFAULT;
+
+ return err;
}
/*
@@ -739,8 +754,7 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
unsigned long vmend;
vma = find_vma(mm, start);
- if (!vma || vma->vm_start > start)
- return -EFAULT;
+ VM_BUG_ON(!vma);
prev = vma->vm_prev;
if (start > vma->vm_start)
--
1.8.3.1
