It took a hell of a lot of digging, but it seems to have started with this thread, way back in 2013.
Now, I'm all for professional communication, and emails can be easy to misinterpret, but this looks like a bit of an over-reaction. Someone commented that they send patches to Greg KH because Linus scares him, but added a winkey smiley afterwards, i.e. not really all that scary. Then Linus made a joke about Greg being big and squishing people that may or may not be playful or insulting, without knowing much about the relationship between these guys it's hard to say. Squish is hardly a word you use when you're really angry though.
And then Linus and Ingo gently tick off Greg and says he should be tougher, Linus says Greg is acting like a "door mat" and says "You may need to learn to say no to people". Ingo says "be frank with contributors and sometimes swear a bit". Probably this discussion would be held off list in a more traditional corporate environment to avoid embarrassing Greg (though "you are too nice" is not that embarrassing), but he takes it in his stride and agrees to be tougher.
OK, so far, just another day in open source land? Well, then Sarah Sharp flies off the handle and says:
Seriously, guys? Is this what we need in order to get improved -stable? Linus Torvalds is advocating for physical intimidation and violence. Ingo Molnar and Linus are advocating for verbal abuse.
Not *fucking* cool. Violence, whether it be physical intimidation, verbal threats or verbal abuse is not acceptable. Keep it professional on the mailing lists.
What the heck? The only thing she could be referring to this thread so far has been Linus talking about Greg being a giant who might "squish you without even noticing". Nobody could seriously interpret that as advocating for violence unless you were so unbelievably literal you'd be unable to handle ordinary conversations.
And then there's the conflation of "verbal abuse" with "violence". These are two words that mean very different things. And finally the assertion that by trying to make jokes (perhaps not very well), Linus and Ingo were being unprofessional. Not surprisingly, Linus had a problem with this claim.
Now I don't know, probably this could have been avoided if the discussion with Greg had been private. But it seems Sharp would have let rip at some other point if someone else made an off-colour joke. I can believe LKML is a tough environment, but this isn't the best evidence possible. Perhaps there have been other incidents, but as Sharp doesn't list any, it's hard to say.