Messages in this thread | | | Date | Wed, 29 Jan 2020 11:26:02 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] locking/osq_lock: fix a data race in osq_wait_next |
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On Wed, Jan 29, 2020 at 07:49:35PM +0100, Peter Zijlstra wrote: > On Tue, Jan 28, 2020 at 04:22:53PM -0800, Paul E. McKenney wrote: > > On Tue, Jan 28, 2020 at 05:56:55PM +0100, Peter Zijlstra wrote: > > > On Tue, Jan 28, 2020 at 12:46:26PM +0100, Marco Elver wrote: > > > > > > > > Marco, any thought on improving KCSAN for this to reduce the false > > > > > positives? > > > > > > > > Define 'false positive'. > > > > > > I'll use it where the code as written is correct while the tool > > > complains about it. > > > > I could be wrong, but I would guess that Marco is looking for something > > a little less subjective and a little more specific. ;-) > > How is that either? If any valid translation by a compile results in > correct functionality, yet the tool complains, then surely we can speak > of a objective fact.
Marco covered my concern in his point about the need to change the compiler.
In any case, agreed, if a read does nothing but feed into the old/new values for a CAS, the only thing a reasonable compiler (as opposed to a just-barely-meets-the-standard demonic compiler) can do to you is to decrease the CAS success rate.
Thanx, Paul
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