On Tue, Jun 18, 2019 at 05:22:15PM +0200, Daniel Vetter wrote: > On Tue, May 21, 2019 at 11:44:11AM -0400, Jerome Glisse wrote: > > On Mon, May 20, 2019 at 11:39:42PM +0200, Daniel Vetter wrote: > > > Just a bit of paranoia, since if we start pushing this deep into > > > callchains it's hard to spot all places where an mmu notifier > > > implementation might fail when it's not allowed to. > > > > > > Inspired by some confusion we had discussing i915 mmu notifiers and > > > whether we could use the newly-introduced return value to handle some > > > corner cases. Until we realized that these are only for when a task > > > has been killed by the oom reaper. > > > > > > An alternative approach would be to split the callback into two > > > versions, one with the int return value, and the other with void > > > return value like in older kernels. But that's a lot more churn for > > > fairly little gain I think. > > > > > > Summary from the m-l discussion on why we want something at warning > > > level: This allows automated tooling in CI to catch bugs without > > > humans having to look at everything. If we just upgrade the existing > > > pr_info to a pr_warn, then we'll have false positives. And as-is, no > > > one will ever spot the problem since it's lost in the massive amounts > > > of overall dmesg noise. > > > > > > v2: Drop the full WARN_ON backtrace in favour of just a pr_warn for > > > the problematic case (Michal Hocko). I disagree with this v2 note, the WARN_ON/WARN will trigger checkers like syzkaller to report a bug, while a random pr_warn probably will not. I do agree the backtrace is not useful here, but we don't have a warn-no-backtrace version.. IMHO, kernel/driver bugs should always be reported by WARN & friends. We never expect to see the print, so why do we care how big it is? Also note that WARN integrates an unlikely() into it so the codegen is automatically a bit more optimal that the if & pr_warn combination. Jason
