On Mon, Aug 6, 2018 at 4:21 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > On Mon 06-08-18 13:57:38, Dmitry Vyukov wrote: >> On Mon, Aug 6, 2018 at 1:02 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > [...] >> >> A much >> >> friendlier for user way to say this would be print a message at the >> >> point of misconfiguration saying what exactly is wrong, e.g. "pid $PID >> >> misconfigures cgroup /cgroup/path with mem.limit=0" without a stack >> >> trace (does not give any useful info for user). And return EINVAL if >> >> it can't fly at all? And then leave the "or a kernel bug" part for the >> >> WARNING each occurrence of which we do want to be reported to kernel >> >> developers. >> > >> > But this is not applicable here. Your misconfiguration is quite obvious >> > because you simply set the hard limit to 0. This is not the only >> > situation when this can happen. There is no clear point to tell, you are >> > doing this wrong. If it was we would do it at that point obviously. >> >> But, isn't there a point were hard limit is set to 0? I would expect >> there is a something like cgroup file write handler with a value of 0 >> or something. > > Yeah, but this is only one instance of the problem. Other is that the > memcg is not reclaimable for any other reasons. And we do not know what > those might be > >> >> > If you have a strong reason to believe that this is an abuse of WARN I >> > am all happy to change that. But I haven't heard any yet, to be honest. >> >> WARN must not be used for anything that is not kernel bugs. If this is >> not kernel bug, WARN must not be used here. > > This is rather strong wording without any backing arguments. I strongly > doubt 90% of existing WARN* match this expectation. WARN* has > traditionally been a way to tell that something suspicious is going on. > Those situation are mostly likely not fatal but it is good to know they > are happening. Today syzbot covers about 1M lines of kernel code, and we fuzz for several years with panic_on_warn=1 and each unique crash is recorded and reported. Over several thousands bugs that we reported, there were maybe 2 dozens of such cases (WARN on invalid user inputs, ENOMEM, etc). The solution always was to remove the WARNING on covert to pr_err. As of now, I see only 2 such cases open: this one and WARN on ENOMEM in input subsystem. Either way, we do badly need this separation. If there are deviations we need to continue fixing them.
