Commit 8402ce61 authored by Daniel Vetter's avatar Daniel Vetter Committed by Jason Gunthorpe

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.chSigned-off-by: default avatarDaniel Vetter <daniel.vetter@intel.com>
Reviewed-by: default avatarJason Gunthorpe <jgg@mellanox.com>
Signed-off-by: default avatarJason Gunthorpe <jgg@mellanox.com>
parent 9b2ed9cb
......@@ -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;
}
}
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment