On Wed, May 29, 2019 at 10:02:43PM +0100, David Howells wrote:

Jann Horn [off-list ref] wrote:

quoted

Does this mean that refcount_read() isn't sufficient for what you want
to do with tracing (because for some reason you actually need to know
the values atomically at the time of increment/decrement)?

Correct.  There's a gap and if an interrupt or something occurs, it's
sufficiently big for the refcount trace to go weird.

I've seen it in afs/rxrpc where the incoming network packets that are part of
the rxrpc call flow disrupt the refcounts noted in trace lines.

Can you re-iterate the exact problem? I konw we talked about this in the
past, but I seem to have misplaced those memories :/

FWIW I agree that kref is useless fluff, but I've long ago given up on
that fight.