On Wed 19-07-17 09:39:50, Mike Kravetz wrote: > On 07/13/2017 12:11 PM, Vlastimil Babka wrote: > > [+CC linux-api] > > > > On 07/13/2017 05:58 PM, Mike Kravetz wrote: > >> mremap will create a 'duplicate' mapping if old_size == 0 is > >> specified. Such duplicate mappings make no sense for private > >> mappings. If duplication is attempted for a private mapping, > >> mremap creates a separate private mapping unrelated to the > >> original mapping and makes no modifications to the original. > >> This is contrary to the purpose of mremap which should return > >> a mapping which is in some way related to the original. > >> > >> Therefore, return EINVAL in the case where if an attempt is > >> made to duplicate a private mapping. > >> > >> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> > > > > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > > After considering Michal's concerns with follow on patch, it appears > this patch provides the most desired behavior. Any other concerns > or issues with this patch? Maybe we should add a pr_warn_once to make users aware that this is no longer supported. > If this moves forward, I will create man page updates to describe the > mremap(old_size == 0) behavior. > > -- > Mike Kravetz > > > > >> --- > >> mm/mremap.c | 7 +++++++ > >> 1 file changed, 7 insertions(+) > >> > >> diff --git a/mm/mremap.c b/mm/mremap.c > >> index cd8a1b1..076f506 100644 > >> --- a/mm/mremap.c > >> +++ b/mm/mremap.c > >> @@ -383,6 +383,13 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, > >> if (!vma || vma->vm_start > addr) > >> return ERR_PTR(-EFAULT); > >> > >> + /* > >> + * !old_len is a special case where a mapping is 'duplicated'. > >> + * Do not allow this for private mappings. Do not allow this for private mappings because we have never really duplicated the range for those so the new VMA is a fresh one unrelated to the original one which breaks mremap semantic. While we can do that there doesn't seem to be any existing usecase currently. > >> + */ > >> + if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) > >> + return ERR_PTR(-EINVAL); > >> + > >> if (is_vm_hugetlb_page(vma)) > >> return ERR_PTR(-EINVAL); > >> > >> > > -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
