The patch titled
Subject: mremap should return -ENOMEM when __vm_enough_memory fail
has been added to the -mm tree. Its filename is
mremap-should-return-enomem-when-__vm_enough_memory-fail.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mremap-should-return-enomem-when-__vm_enough_memory-fail.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mremap-should-return-enomem-when-__vm_enough_memory-fail.patch
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From: Derek <denc716@xxxxxxxxx>
Subject: mremap should return -ENOMEM when __vm_enough_memory fail
Recently I straced bash behavior in this dd zero pipe to read test, in
part of testing under vm.overcommit_memory=2 (OVERCOMMIT_NEVER mode):
# dd if=/dev/zero | read x
The bash sub shell is calling mremap to reallocate more and more memory
untill it finally failed -ENOMEM (I expect), or to be killed by system OOM
killer (which should not happen under OVERCOMMIT_NEVER mode); But the
mremap system call actually failed of -EFAULT, which is a surprise to me,
I think it's supposed to be -ENOMEM? then I wrote this piece of C code
testing confirmed it: https://gist.github.com/crquan/326bde37e1ddda8effe5
$ ./remap
allocated one page @0x7f686bf71000, (PAGE_SIZE: 4096)
grabbed 7680512000 bytes of memory (1875125 pages) @ 00007f6690993000.
mremap failed Bad address (14).
The -EFAULT comes from the branch of security_vm_enough_memory_mm failure,
underlyingly it calls __vm_enough_memory which returns only 0 for success
or -ENOMEM; So why vma_to_resize needs to return -EFAULT in this case?
this sounds like a mistake to me.
Some more digging into git history:
1) Before commit 119f657c7 ("RLIMIT_AS checking fix") in May 1 2005
(pre 2.6.12 days) it was returning -ENOMEM for this failure;
2) but commit 119f657c7 ("untangling do_mremap(), part 1") changed it
accidentally, to what ever is preserved in local ret, which happened to
be -EFAULT, in a previous assignment;
3) then in commit 54f5de709 code refactoring, it's explicitly returning
-EFAULT, should be wrong.
Signed-off-by: Derek Che <crquan@xxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mremap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/mremap.c~mremap-should-return-enomem-when-__vm_enough_memory-fail mm/mremap.c
--- a/mm/mremap.c~mremap-should-return-enomem-when-__vm_enough_memory-fail
+++ a/mm/mremap.c
@@ -375,7 +375,7 @@ static struct vm_area_struct *vma_to_res
if (vma->vm_flags & VM_ACCOUNT) {
unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
if (security_vm_enough_memory_mm(mm, charged))
- goto Efault;
+ goto Enomem;
*p = charged;
}
_
Patches currently in -mm which might be from denc716@xxxxxxxxx are
mremap-should-return-enomem-when-__vm_enough_memory-fail.patch
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