[PATCH tip/core/rcu 07/19] scftorture: Add smp_call_function_single() memory-ordering checks

paulmck
2020-08-31T18:09:27Z

This commit adds checks for memory misordering across calls to
smp_call_function_single() and also across returns in the case where
the caller waits. Misordering results in a splat.

[ paulmck: s/GFP_KERNEL/GFP_ATOMIC/ per kernel test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/scftorture.c | 56 +++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 48 insertions(+), 8 deletions(-)

diff --git a/kernel/scftorture.c b/kernel/scftorture.c
index 09a6242..9b42271 100644
--- a/kernel/scftorture.c
+++ b/kernel/scftorture.c
@@ -117,9 +117,20 @@ static struct scf_selector scf_sel_array[SCF_NPRIMS];
static int scf_sel_array_len;
static unsigned long scf_sel_totweight;

+// Communicate between caller and handler.
+struct scf_check {
+ bool scfc_in;
+ bool scfc_out;
+ int scfc_cpu; // -1 for not _single().
+ bool scfc_wait;
+};
+
// Use to wait for all threads to start.
static atomic_t n_started;
static atomic_t n_errs;
+static atomic_t n_mb_in_errs;
+static atomic_t n_mb_out_errs;
+static atomic_t n_alloc_errs;
static bool scfdone;

DEFINE_TORTURE_RANDOM_PERCPU(scf_torture_rand);
@@ -222,24 +233,27 @@ static struct scf_selector *scf_sel_rand(struct torture_random_state *trsp)
// Update statistics and occasionally burn up mass quantities of CPU time,
// if told to do so via scftorture.longwait. Otherwise, occasionally burn
// a little bit.
-static void scf_handler(void *unused)
+static void scf_handler(void *scfc_in)
{
int i;
int j;
unsigned long r = torture_random(this_cpu_ptr(&scf_torture_rand));
+ struct scf_check *scfcp = scfc_in;

+ if (likely(scfcp) && WARN_ON_ONCE(unlikely(!READ_ONCE(scfcp->scfc_in))))
+ atomic_inc(&n_mb_in_errs);
this_cpu_inc(scf_invoked_count);
if (longwait <= 0) {
if (!(r & 0xffc0))
udelay(r & 0x3f);
- return;
+ goto out;
}
if (r & 0xfff)
- return;
+ goto out;
r = (r >> 12);
if (longwait <= 0) {
udelay((r & 0xff) + 1);
- return;
+ goto out;
}
r = r % longwait + 1;
for (i = 0; i < r; i++) {
@@ -248,14 +262,24 @@ static void scf_handler(void *unused)
cpu_relax();
}
}
+out:
+ if (unlikely(!scfcp))
+ return;
+ if (scfcp->scfc_wait)
+ WRITE_ONCE(scfcp->scfc_out, true);
+ else
+ kfree(scfcp);
}

// As above, but check for correct CPU.
-static void scf_handler_1(void *me)
+static void scf_handler_1(void *scfc_in)
{
- if (WARN_ON_ONCE(smp_processor_id() != (uintptr_t)me))
+ struct scf_check *scfcp = scfc_in;
+
+ if (likely(scfcp) && WARN_ONCE(smp_processor_id() != scfcp->scfc_cpu, "%s: Wanted CPU %d got CPU %d\n", __func__, scfcp->scfc_cpu, smp_processor_id())) {
atomic_inc(&n_errs);
- scf_handler(NULL);
+ }
+ scf_handler(scfcp);
}

// Randomly do an smp_call_function*() invocation.
@@ -263,6 +287,7 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
{
uintptr_t cpu;
int ret;
+ struct scf_check *scfcp = NULL;
struct scf_selector *scfsp = scf_sel_rand(trsp);

if (use_cpus_read_lock)
@@ -271,17 +296,32 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
preempt_disable();
switch (scfsp->scfs_prim) {
case SCF_PRIM_SINGLE:
+ scfcp = kmalloc(sizeof(*scfcp), GFP_ATOMIC);
+ if (WARN_ON_ONCE(!scfcp))
+ atomic_inc(&n_alloc_errs);
cpu = torture_random(trsp) % nr_cpu_ids;
if (scfsp->scfs_wait)
scfp->n_single_wait++;
else
scfp->n_single++;
- ret = smp_call_function_single(cpu, scf_handler_1, (void *)cpu, scfsp->scfs_wait);
+ if (scfcp) {
+ scfcp->scfc_cpu = cpu;
+ scfcp->scfc_wait = scfsp->scfs_wait;
+ scfcp->scfc_out = false;
+ scfcp->scfc_in = true;
+ }
+ ret = smp_call_function_single(cpu, scf_handler_1, (void *)scfcp, scfsp->scfs_wait);
if (ret) {
if (scfsp->scfs_wait)
scfp->n_single_wait_ofl++;
else
scfp->n_single_ofl++;
+ kfree(scfcp);
+ } else if (scfcp && scfsp->scfs_wait) {
+ if (WARN_ON_ONCE(!scfcp->scfc_out))
+ atomic_inc(&n_mb_out_errs); // Leak rather than trash!
+ else
+ kfree(scfcp);
}
break;
case SCF_PRIM_MANY:
--
2.9.5