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mm/mmap: regression fix for unmapped_area{_topdown} 

The maple tree limits the gap returned to a window that specifically fits
what was asked.  This may not be optimal in the case of switching search
directions or a gap that does not satisfy the requested space for other
reasons.  Fix the search by retrying the operation and limiting the search
window in the rare occasion that a conflict occurs.

Link: https://lkml.kernel.org/r/20230414185919.4175572-1-Liam.Howlett@oracle.com
Fixes: 3499a13168 ("mm/mmap: use maple tree for unmapped_area{_topdown}")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Liam R. Howlett 2023-04-14 14:59:19 -04:00 committed by Andrew Morton
parent 06e8fd9993
commit 58c5d0d6d5
1 changed files with 43 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
mm/mmap.c
View File

@ -1518,7 +1518,8 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
*/
static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
{
unsigned long length, gap;
unsigned long length, gap, low_limit;
struct vm_area_struct *tmp;
MA_STATE(mas, &current->mm->mm_mt, 0, 0);
@ -1527,12 +1528,29 @@ static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
if (length < info->length)
return -ENOMEM;
if (mas_empty_area(&mas, info->low_limit, info->high_limit - 1,
length))
low_limit = info->low_limit;
retry:
if (mas_empty_area(&mas, low_limit, info->high_limit - 1, length))
return -ENOMEM;
gap = mas.index;
gap += (info->align_offset - gap) & info->align_mask;
tmp = mas_next(&mas, ULONG_MAX);
if (tmp && (tmp->vm_flags & VM_GROWSDOWN)) { /* Avoid prev check if possible */
if (vm_start_gap(tmp) < gap + length - 1) {
low_limit = tmp->vm_end;
mas_reset(&mas);
goto retry;
}
} else {
tmp = mas_prev(&mas, 0);
if (tmp && vm_end_gap(tmp) > gap) {
low_limit = vm_end_gap(tmp);
mas_reset(&mas);
goto retry;
}
}
return gap;
}
@ -1548,7 +1566,8 @@ static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
*/
static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
{
unsigned long length, gap;
unsigned long length, gap, high_limit, gap_end;
struct vm_area_struct *tmp;
MA_STATE(mas, &current->mm->mm_mt, 0, 0);
/* Adjust search length to account for worst case alignment overhead */
@ -1556,12 +1575,31 @@ static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
if (length < info->length)
return -ENOMEM;
if (mas_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
high_limit = info->high_limit;
retry:
if (mas_empty_area_rev(&mas, info->low_limit, high_limit - 1,
length))
return -ENOMEM;
gap = mas.last + 1 - info->length;
gap -= (gap - info->align_offset) & info->align_mask;
gap_end = mas.last;
tmp = mas_next(&mas, ULONG_MAX);
if (tmp && (tmp->vm_flags & VM_GROWSDOWN)) { /* Avoid prev check if possible */
if (vm_start_gap(tmp) <= gap_end) {
high_limit = vm_start_gap(tmp);
mas_reset(&mas);
goto retry;
}
} else {
tmp = mas_prev(&mas, 0);
if (tmp && vm_end_gap(tmp) > gap) {
high_limit = tmp->vm_start;
mas_reset(&mas);
goto retry;
}
}
return gap;
}