Re: [PATCH v2] fs: Convert return type int to vm_fault_t

[Matthew Wilcox]

On Mon, Sep 03, 2018 at 05:28:43PM -0700, Andrew Morton wrote:
> > > I'm beginning to feel vm_fault_t exhaustion.  Please remind me what
> > > benefit we're going to get out of all this churn?

Hi Andrew,

The primary benefit is to help driver writers.  At the moment, there
is nothing to stop them returning -ENOMEM instead of VM_FAULT_NOMEM.
There were one or two examples of this in the tree, but I think they're
all gone now.

Secondarily, there are a number of places which translate between error
codes and vm_fault codes.  Those places are reduced as a result of these
patches, if not entirely eliminated yet.  There was some pretty extreme
cargo-culting of errno to vm_fault switch statements, particularly in
the DRM drivers.

There were also several places which were just ignoring the return value
of vm_insert_foo(), and as a result of this audit, those have been fixed.
Those errors are going to be rare, but can cause inappropriate decisions
to be made by the OOM killer.

Now that I think about it, vmf_insert_foo() should probably get marked
with __must_check to prevent those kinds of errors from being introduced
again.