From 8402ce61bec28a1b73ec467b4c146f1e3f587044 Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Wed, 14 Aug 2019 22:20:23 +0200 Subject: [PATCH] mm/mmu_notifiers: check if mmu notifier callbacks are allowed to fail 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. Link: https://lore.kernel.org/r/20190814202027.18735-2-daniel.vetter@ffwll.ch Signed-off-by: Daniel Vetter Reviewed-by: Jason Gunthorpe Signed-off-by: Jason Gunthorpe --- mm/mmu_notifier.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c index 9e92ec8006fc..d76ea27e2bbb 100644 --- a/mm/mmu_notifier.c +++ b/mm/mmu_notifier.c @@ -179,6 +179,8 @@ int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range) pr_info("%pS callback failed with %d in %sblockable context.\n", mn->ops->invalidate_range_start, _ret, !mmu_notifier_range_blockable(range) ? "non-" : ""); + WARN_ON(mmu_notifier_range_blockable(range) || + ret != -EAGAIN); ret = _ret; } }