472e8c55cf
Successful RMW operations are supposed to be fully ordered, but Alpha's xchg() and cmpxchg() do not meet this requirement. Will Deacon noticed the bug: > So MP using xchg: > > WRITE_ONCE(x, 1) > xchg(y, 1) > > smp_load_acquire(y) == 1 > READ_ONCE(x) == 0 > > would be allowed. ... which thus violates the above requirement. Fix it by adding a leading smp_mb() to the xchg() and cmpxchg() implementations. Reported-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Matt Turner <mattst88@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Richard Henderson <rth@twiddle.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-alpha@vger.kernel.org Link: http://lkml.kernel.org/r/1519291488-5752-1-git-send-email-parri.andrea@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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