On Tue, 24 Apr 2018, Michal Hocko wrote:
> On Tue 24-04-18 13:00:11, Mikulas Patocka wrote: > > > > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > On Tue 24-04-18 11:50:30, Mikulas Patocka wrote: > > > > > > > > > > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > > > > > On Mon 23-04-18 20:06:16, Mikulas Patocka wrote: > > > > > [...] > > > > > > @@ -404,6 +405,12 @@ void *kvmalloc_node(size_t size, gfp_t f > > > > > > */ > > > > > > WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL); > > > > > > > > > > > > +#ifdef CONFIG_DEBUG_SG > > > > > > + /* Catch bugs when the caller uses DMA API on the result of > > > > > > kvmalloc. */ > > > > > > + if (!(prandom_u32_max(2) & 1)) > > > > > > + goto do_vmalloc; > > > > > > +#endif > > > > > > > > > > I really do not think there is anything DEBUG_SG specific here. Why > > > > > you > > > > > simply do not follow should_failslab path or even reuse the function? > > > > > > > > CONFIG_DEBUG_SG is enabled by default in RHEL and Fedora debug kernel > > > > (if > > > > you don't like CONFIG_DEBUG_SG, pick any other option that is enabled > > > > there). > > > > > > Are you telling me that you are shaping a debugging functionality basing > > > on what RHEL has enabled? And you call me evil. This is just rediculous. > > > > > > > Fail-injection framework is if off by default and it must be explicitly > > > > enabled and configured by the user - and most users won't enable it. > > > > > > It can be enabled easily. And if you care enough for your debugging > > > kernel then just make it enabled unconditionally. > > > > So, should we add a new option CONFIG_KVMALLOC_FALLBACK_DEFAULT? I'm not > > quite sure if 3 lines of debugging code need an extra option, but if you > > don't want to reuse any existing debug option, it may be possible. Adding > > it to the RHEL debug kernel would be trivial. > > Wouldn't it be equally trivial to simply enable the fault injection? You > would get additional failure paths testing as a bonus. The RHEL and Fedora debugging kernels are compiled with fault injection. But the fault-injection framework will do nothing unless it is enabled by a kernel parameter or debugfs write. Most users don't know about the fault injection kernel parameters or debugfs files and won't enabled it. We need a CONFIG_ option to enable it by default in the debugging kernels (and we could add a kernel parameter to override the default, fine-tune the fallback probability etc.) Mikulas
