On Fri, Apr 15, 2022 at 4:04 PM Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, Apr 15, 2022 at 3:58 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > > > BUG_ONs are harmful but problems that trigger them would be > > presummingly less penetrating to the user base; on the other hand, > > from my experience working with some testers (ordinary users), they > > ignore WARN_ON_ONCEs until the kernel crashes. > > I don't understand your argument. > > First you say that VM_BUG_ON() is only for VM developers. > > Then you say "some testers (ordinary users) ignore WARN_ON_ONCEs until > the kernel crashes". > > So which is it? > > VM developers, or ordinary users? > > Honestly, if a VM developer is ignoring a WARN_ON_ONCE() from the VM > subsystem, I don't even know what to say. > > And for ordinary users, a WARN_ON_ONCE() is about a million times > better, becasue: > > - the machine will hopefully continue working, so they can report the warning > > - even when they don't notice them, distros tend to have automated > reporting infrastructure > > That's why I absolutely *DETEST* those stupid BUG_ON() cases - they > will often kill the machine with nasty locks held, resulting in a > completely undebuggable thing that never gets reported. > > Yes, you can be careful and only put BUG_ON() in places where recovery > is possible. But even then, they have no actual _advantages_ over just > a WARN_ON_ONCE. Generally agreed, and not to belabor this relatively small issue, but in some environments like cloud or managed client deployments, a crash can actually be preferable so we can get a dump, reboot the machine, and get things going again for the application or user, then debug offline. So having the flexibility to do that in those situations is helpful. And there, a full crash dump is better than just a log report with the WARN info, since debugging may be easier with all the kernel memory. Jesse
