On 9/24/21 10:55 AM, Michal Hocko wrote: > On Thu 23-09-21 09:49:57, Vasily Averin wrote: > [...] >> I'm agree that vmalloc callers should expect and handle single vnalloc failures. >> I think it is acceptable to enable fatal_signal_pending check to quickly >> detect such kind of iussues. >> However fatal_signal_pending check can cause serial vmalloc failures >> and I doubt it is acceptable. >> >> Rollback after failed vmalloc can call new vmalloc calls that will be failed too, >> even properly handled such serial failures can cause troubles. > > Could you be more specific? Also how would this be any different from > similar failures for an oom victim? Except that the later is less likely > so (as already mentioend) any potential bugs would be just lurking there > for a longer time. > >> Hypothetically, cancelled vmalloc called inside some filesystem's transaction >> forces its rollback, that in own turn it can call own vmalloc. > > Do you have any specific example? No, it was pure hypothetical assumption. I was thinking about it over the weekend, and decided that: a) such kind of issue (i.e. vmalloc call in rollback after failed vmalloc) is very unlikely b) if it still exists -- it must have own failback with kmalloc(NOFAIL) or just accept/ignore such failure and should not lead to critical failures. If this still happen -- ihis is a bug, we should detect and fix it ASAP. >> Should we perhaps interrupt the first vmalloc only? > > This doesn't make much sense to me TBH. It doesn't address the very > problem you are describing in the changelog. Last question: how do you think, should we perhaps, instead, detect such vmallocs (called in rollback after failed vmalloc) and generate a warnings, to prevent such kind of problems in future? Thank you, Vasily Averin
