On Sat, 2014-02-22 at 14:03 -0500, Peter Hurley wrote: > If it is necessary for a RELEASE-ACQUIRE pair to produce a full barrier, the > ACQUIRE can be followed by an smp_mb__after_unlock_lock() invocation. This > will produce a full barrier if either (a) the RELEASE and the ACQUIRE are > executed by the same CPU or task, or (b) the RELEASE and ACQUIRE act on the > same variable. The smp_mb__after_unlock_lock() primitive is free on many > architectures. Without smp_mb__after_unlock_lock(), the critical sections > corresponding to the RELEASE and the ACQUIRE can cross: > > *A = a; > RELEASE M > ACQUIRE N > *B = b; > > could occur as: > > ACQUIRE N, STORE *B, STORE *A, RELEASE M Ah, OK, that's an error in the documentation. The example should read *A = a; RELEASE *N* ACQUIRE *M* *B = b; The point being you can't have speculation that entangles critical sections, as I've been saying, because that would speculate you into ABBA deadlocks. Paul McKenny will submit a patch fixing the bug in documentation. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
