From ee7035d29576dcb59b1191e5f609517cacab1e56 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 1 Jul 2020 16:38:16 -0700 Subject: 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: Paul E. McKenney --- kernel/scftorture.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'kernel/scftorture.c') diff --git a/kernel/scftorture.c b/kernel/scftorture.c index 880c2cef13e7..83496810fc48 100644 --- a/kernel/scftorture.c +++ b/kernel/scftorture.c @@ -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(); -- cgit v1.2.3