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Subject[PATCH 1/2] mm: fix the racy mm->locked_vm change in
"mm->locked_vm += grow" and vm_stat_account() in acct_stack_growth()
are not safe; multiple threads using the same ->mm can do this at the
same time trying to expans different vma's under down_read(mmap_sem).
This means that one of the "locked_vm += grow" changes can be lost
and we can miss munlock_vma_pages_all() later.

Move this code into the caller(s) under mm->page_table_lock. All other
updates to ->locked_vm hold mmap_sem for writing.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
mm/mmap.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 8393580..4efdc37 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2138,10 +2138,6 @@ static int acct_stack_growth(struct vm_area_struct *vma, unsigned long size, uns
if (security_vm_enough_memory_mm(mm, grow))
return -ENOMEM;

- /* Ok, everything looks good - let it rip */
- if (vma->vm_flags & VM_LOCKED)
- mm->locked_vm += grow;
- vm_stat_account(mm, vma->vm_flags, vma->vm_file, grow);
return 0;
}

@@ -2202,6 +2198,10 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
* against concurrent vma expansions.
*/
spin_lock(&vma->vm_mm->page_table_lock);
+ if (vma->vm_flags & VM_LOCKED)
+ vma->vm_mm->locked_vm += grow;
+ vm_stat_account(vma->vm_mm, vma->vm_flags,
+ vma->vm_file, grow);
anon_vma_interval_tree_pre_update_vma(vma);
vma->vm_end = address;
anon_vma_interval_tree_post_update_vma(vma);
@@ -2273,6 +2273,10 @@ int expand_downwards(struct vm_area_struct *vma,
* against concurrent vma expansions.
*/
spin_lock(&vma->vm_mm->page_table_lock);
+ if (vma->vm_flags & VM_LOCKED)
+ vma->vm_mm->locked_vm += grow;
+ vm_stat_account(vma->vm_mm, vma->vm_flags,
+ vma->vm_file, grow);
anon_vma_interval_tree_pre_update_vma(vma);
vma->vm_start = address;
vma->vm_pgoff -= grow;
--
2.4.3


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