On 03/07/2018 08:25 PM, Mike Kravetz wrote: > On 03/07/2018 05:35 PM, Yisheng Xie wrote: >> However, region_chg makes me a litter puzzle that when its return value < 0, >> sometime >> adds_in_progress is added like this case, while sometime it is not. so why >> not just >> change at the beginning of region_chg ? >> if (f > t) >> return -EINVAL; > > If region_chg returns a value < 0, this indicates an error and > adds_in_progress > should not be incremented. In the case of this bug, region_chg was passed > values where f > t. Of course, this should never happen. But, because it > assumed f <= t, it returned a negative count needed huge page reservations. > The calling code interpreted the negative value as an error and a subsequent > region_add or region_abort. > > I am not opposed to adding the suggested "if (f > t)". However, the > region tracking routines are simple helpers only used by the hugetlbfs > code and the assumption is that they are being called correctly. As > such, I would prefer to leave off the check. But, this is the second > time they have been called incorrectly due to insufficient argument > checking. If we do add this to region_chg, I would also add the check > to all region_* routines for consistency.
I really did not want to add the (f > t) check to the region_* routines. As mentioned we should never encounter this condition. Adding the check here says that we missed discovering an error at higher levels. Therefore, I went back and examined the callers of region_chg. There are only 2: hugetlb_reserve_pages and __vma_reservation_common. hugetlb_reserve_pages is called to set up a reservation for a mapping. __vma_reservation_common is called to check on an existing reservation, and only operates on a single huge page. With this in mind, a check in hugetlb_reserve_pages would be sufficient. Therefore, I added an explicit check to that routine and printed a warning if ever encountered. > I will send out a V2 of this patch tomorrow with the corrected overflow > checking and possibly checks added to the region_* routines. v2 will be sent shortly. In v2 I Cc stable as this is an issue for stable branches as well. -- Mike Kravetz
