[PATCH] KEYS: fix race between updating and finding negative key

Eric Biggers [off-list ref] wrote:

Fix the bug by moving ->reject_error out of the union with ->payload,
then using nonzero ->reject_error to mean that the key is negative.

This eliminates the need for KEY_FLAG_NEGATIVE, which we remove as well
so that we don't have to handle memory ordering between
KEY_FLAG_NEGATIVE and ->reject_error.  We *do* still need to handle
memory ordering between KEY_FLAG_INSTANTIATED and ->reject_error, but
that was needed before (and for KEY_FLAG_NEGATIVE as well --- though it
wasn't done correctly, which was another bug).

Hmmm...  My only objection is that it extends struct key still further, but
you do have a point.

If we're going to do this, can we eliminate KEY_FLAG_INSTANTIATED also and
make ->reject_error into ->status?

	0	-> uninstantiated
	1	-> instantiated
	<0	-> negatively instantiated/rejected

Also, can we make it a short int please?

Also, can setting this field be done with a release barrier rather than a
write barrier?

David
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