Commit ee7035d2 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

scftorture: Prevent compiler from reducing race probabilities 



Detecting smp_call_function() memory misordering requires close timing,
so it is necessary to have the checks immediately before and after
the call to the smp_call_function*() function under test.  This commit
therefore inserts barrier() calls to prevent the compiler from optimizing
memory-misordering detection down into the zone of extreme improbability.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent dbf83b65

kernel/scftorture.c

+8 −2
Original line number Diff line number Diff line
@@ -322,6 +322,7 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra 
			scfp->n_single++;

		if (scfcp) {

			scfcp->scfc_cpu = cpu;

			barrier(); // Prevent race-reduction compiler optimizations.

			scfcp->scfc_in = true;

		}

		ret = smp_call_function_single(cpu, scf_handler_1, (void *)scfcp, scfsp->scfs_wait);
@@ -339,8 +340,10 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra 
			scfp->n_many_wait++;

		else

			scfp->n_many++;

		if (scfcp)

		if (scfcp) {

			barrier(); // Prevent race-reduction compiler optimizations.

			scfcp->scfc_in = true;

		}

		smp_call_function_many(cpu_online_mask, scf_handler, scfcp, scfsp->scfs_wait);

		break;

	case SCF_PRIM_ALL:
@@ -348,8 +351,10 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra 
			scfp->n_all_wait++;

		else

			scfp->n_all++;

		if (scfcp)

		if (scfcp) {

			barrier(); // Prevent race-reduction compiler optimizations.

			scfcp->scfc_in = true;

		}

		smp_call_function(scf_handler, scfcp, scfsp->scfs_wait);

		break;

	}
@@ -358,6 +363,7 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra 
			atomic_inc(&n_mb_out_errs); // Leak rather than trash!

		else

			kfree(scfcp);

		barrier(); // Prevent race-reduction compiler optimizations.

	}

	if (use_cpus_read_lock)

		cpus_read_unlock();

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