On Mon, 6 Jun 2022 at 14:39, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote: > > On Sat, Jun 04, 2022 at 10:32:46AM +0200, 'Dmitry Vyukov' via syzkaller-bugs wrote: > > On Fri, 3 Jun 2022 at 18:12, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > But again, is this a "real and able to be triggered from userspace" > > > problem, or just fault-injection-induced? > > > > Then this is something to fix in the fault injection subsystem. > > Testing systems shouldn't be reporting false positives. > > What allocations cannot fail in real life? Is it <=page_size? > > > > Apparently in 2014, anything less than *EIGHT?!!* pages succeeded! > > https://lwn.net/Articles/627419/ > > I have been on the look out since that article and never seen anyone > mention it changing. I think we should ignore that and say that > anything over PAGE_SIZE can fail. Possibly we could go smaller than > PAGE_SIZE... +linux-mm for GFP expertise re what allocations cannot possibly fail and should be excluded from fault injection. Interesting, thanks for the link. PAGE_SIZE looks like a good start. Once we have the predicate in place, we can refine it later when/if we have more inputs. But I wonder about GFP flags. They definitely have some impact on allocations. If GFP_ACCOUNT is set, all allocations can fail, right? If GFP_DMA/DMA32 is set, allocations can fail, right? What about other zones? If GFP_NORETRY is set, allocations can fail? What about GFP_NOMEMALLOC and GFP_ATOMIC? What about GFP_IO/GFP_FS/GFP_DIRECT_RECLAIM/GFP_KSWAPD_RECLAIM? At least some of these need to be set for allocations to not fail? Which ones? Any other flags are required to be set/unset for allocations to not fail? FTR here is quick link to flags list: https://elixir.bootlin.com/linux/v5.19-rc1/source/include/linux/gfp.h#L32
