On 8/7/20 7:28 AM, Wei Yang wrote: > On Fri, Aug 07, 2020 at 08:49:51PM +0800, Baoquan He wrote: >> On 08/07/20 at 05:12pm, Wei Yang wrote: >>> list_first_entry() may not return NULL even when the list is empty. >>> >>> Let's make sure the behavior by using list_first_entry_or_null(), >>> otherwise it would corrupt the list. >>> >>> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> >>> --- >>> mm/hugetlb.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>> index 62ec74f6d03f..0a2f3851b828 100644 >>> --- a/mm/hugetlb.c >>> +++ b/mm/hugetlb.c >>> @@ -237,7 +237,8 @@ get_file_region_entry_from_cache(struct resv_map *resv, long from, long to) >>> VM_BUG_ON(resv->region_cache_count <= 0); >> >> >> We have had above line, is it possible to be NULL from list_first_entry? >> >>> >>> resv->region_cache_count--; >>> - nrg = list_first_entry(&resv->region_cache, struct file_region, link); >>> + nrg = list_first_entry_or_null(&resv->region_cache, >>> + struct file_region, link); >>> VM_BUG_ON(!nrg); > > Or we can remove this VM_BUG_ON()? > I would prefer that we just remove the 'VM_BUG_ON(!nrg)'. Code elsewhere is responsible for making sure there is ALWAYS an entry in the cache. That is why the 'VM_BUG_ON(resv->region_cache_count <= 0)' is at the beginning of the routine. -- Mike Kravetz
