[PATCH 1/3] mm: shift VM_GROWS* check from mmap_region() todo_mmap_pgoff()

From: Oleg Nesterov
Date: Sun Jul 14 2013 - 13:00:29 EST


mmap() doesn't allow the non-anonymous mappings with VM_GROWS* bit set.
In particular this means that mmap_region()->vma_merge(file, vm_flags)
must always fail if vm_flags & VM_GROWS. So it does not make sense to
check VM_GROWS* after we already allocated the new vma, the only caller,
do_mmap_pgoff(), which can pass this flag can do the check itself.

And this looks a bit more correct, mmap_region() already unmapped the
old mapping at this stage. But if mmap() is going to fail, it should
avoid do_munmap() if possible.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
mm/mmap.c | 9 +++------
1 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index f681e18..6b69352 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1327,6 +1327,9 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
}
}

+ /* Only MAP_PRIVATE|MAP_ANONYMOUS can use MAP_GROWS */
+ if ((vm_flags & VM_MAYSHARE) && (vm_flags & (VM_GROWSDOWN|VM_GROWSUP)))
+ return -EINVAL;
/*
* Set 'VM_NORESERVE' if we should not account for the
* memory use of this mapping.
@@ -1542,11 +1545,7 @@ munmap_back:
vma->vm_pgoff = pgoff;
INIT_LIST_HEAD(&vma->anon_vma_chain);

- error = -EINVAL; /* when rejecting VM_GROWSDOWN|VM_GROWSUP */
-
if (file) {
- if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
- goto free_vma;
if (vm_flags & VM_DENYWRITE) {
error = deny_write_access(file);
if (error)
@@ -1571,8 +1570,6 @@ munmap_back:
pgoff = vma->vm_pgoff;
vm_flags = vma->vm_flags;
} else if (vm_flags & VM_SHARED) {
- if (unlikely(vm_flags & (VM_GROWSDOWN|VM_GROWSUP)))
- goto free_vma;
error = shmem_zero_setup(vma);
if (error)
goto free_vma;
--
1.5.5.1

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