On Fri, 13 Mar 2015, Derek wrote: > 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 > > 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? > it sounds like a mistake to me. > > Some more digging into git history: > 1) Before commit 119f657c7 in May 1 2005 (pre 2.6.12 days) it was returning > -ENOMEM for this failure; > 2) but commit 119f657c7 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> vma_to_resize() could certainly be cleaned up to just return ERR_PTR() and avoiding the "goto"s since there is no other cleanup needed as suggested by Kirill if you have time for a cleanup patch on top of this. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>