pkg/bisect: rollback the guilty commit and test about syzkaller HOT 6 CLOSED

Take the kernel at the identified revision and revert it.

We already done this check during bisection.

Reverting at HEAD may give some additional info, but not sure if it will be useful.
Kernel commits are not reverted often. We also don't know the tree maintainer is interested in, e.g. maintainer may consider reverting on sound tree, but we tested on usb.
Or it may not revert cleanly, or trap on another bug, or the automatic revert may introduce a new bug.

from syzkaller.

We already done this check during bisection.

You mean in detectNoopChange()? We compare kernel signatures, but we don't run the reproducer.

from syzkaller.

I mean the bisection itself. It's literally what bisection is checking: the bug happens on the resulting commit, but not on the previous one (which is effectively reverting the guilty commit).

from syzkaller.

It's literally what bisection is checking: the bug happens on the resulting commit

Yes, but it's only true assuming that we were able to give a 100% correct answer at every bisection step, which is not always the case.

from syzkaller.

I assumed bisection cannot point to a commit w/o testing on that commit with positive results and testing on the previous one with negative result, regardless of results on all previous steps. And that's effectively testing a revert. In all other cases bisection points to multiple commits, which we don't report.

from syzkaller.

Hmm, indeed! Thanks.

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