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scftorture: Prevent compiler from reducing race probabilities

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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 <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-07-01 16:38:16 -07:00
parent dbf83b655a
commit ee7035d295
1 changed files with 8 additions and 2 deletions
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10
kernel/scftorture.c
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@ -322,6 +322,7 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
scfp->n_single++; scfp->n_single++;
if (scfcp) { if (scfcp) {
scfcp->scfc_cpu = cpu; scfcp->scfc_cpu = cpu;
barrier(); // Prevent race-reduction compiler optimizations.
scfcp->scfc_in = true; scfcp->scfc_in = true;
} }
ret = smp_call_function_single(cpu, scf_handler_1, (void *)scfcp, scfsp->scfs_wait); 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++; scfp->n_many_wait++;
else else
scfp->n_many++; scfp->n_many++;
if (scfcp) if (scfcp) {
barrier(); // Prevent race-reduction compiler optimizations.
scfcp->scfc_in = true; scfcp->scfc_in = true;
}
smp_call_function_many(cpu_online_mask, scf_handler, scfcp, scfsp->scfs_wait); smp_call_function_many(cpu_online_mask, scf_handler, scfcp, scfsp->scfs_wait);
break; break;
case SCF_PRIM_ALL: case SCF_PRIM_ALL:
@ -348,8 +351,10 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
scfp->n_all_wait++; scfp->n_all_wait++;
else else
scfp->n_all++; scfp->n_all++;
if (scfcp) if (scfcp) {
barrier(); // Prevent race-reduction compiler optimizations.
scfcp->scfc_in = true; scfcp->scfc_in = true;
}
smp_call_function(scf_handler, scfcp, scfsp->scfs_wait); smp_call_function(scf_handler, scfcp, scfsp->scfs_wait);
break; 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! atomic_inc(&n_mb_out_errs); // Leak rather than trash!
else else
kfree(scfcp); kfree(scfcp);
barrier(); // Prevent race-reduction compiler optimizations.
} }
if (use_cpus_read_lock) if (use_cpus_read_lock)
cpus_read_unlock(); cpus_read_unlock();