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 commit119f657c7
("RLIMIT_AS checking fix") in May 1 2005 (pre 2.6.12 days) it was returning -ENOMEM for this failure; 2) but commit119f657c7
("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 commit54f5de709
code refactoring, it's explicitly returning -EFAULT, should be wrong. Signed-off-by: Derek Che <crquan@ymail.com> Acked-by: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -381,7 +381,7 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
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if (vma->vm_flags & VM_ACCOUNT) {
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unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
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if (security_vm_enough_memory_mm(mm, charged))
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goto Efault;
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goto Enomem;
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*p = charged;
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}
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