On Tue, 17 Mar 2015, denc716@xxxxxxxxx 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 > > $ ./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 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: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Did Kirill ack this patch? > --- > mm/mremap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/mremap.c b/mm/mremap.c > index 57dadc0..5da81cb 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -375,7 +375,7 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, > 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; > } The patch is corrupted and won't apply because there aren't three lines after the changed line. -- 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>