locking/locktorture: Fix num reader/writer corner cases

Things can explode for locktorture if the user does combinations
of nwriters_stress=0 nreaders_stress=0. Fix this by not assuming
we always want to torture writer threads.

Reported-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>

1 files changed, 44 insertions, 32 deletions

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index a307a79e6b0b..2a1fc2a58910 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -703,8 +703,7 @@ static void __torture_print_stats(char *page,
 {
         bool fail = 0;
         int i, n_stress;
-        long max = 0;
-        long min = statp[0].n_lock_acquired;
+        long max = 0, min = statp ? statp[0].n_lock_acquired : 0;
         long long sum = 0;
 
         n_stress = write ? cxt.nrealwriters_stress : cxt.nrealreaders_stress;
@@ -811,7 +810,7 @@ static void lock_torture_cleanup(void)
          * such, only perform the underlying torture-specific cleanups,
          * and avoid anything related to locktorture.
          */
-        if (!cxt.lwsa)
+        if (!cxt.lwsa && !cxt.lrsa)
                 goto end;
 
         if (writer_tasks) {
@@ -886,6 +885,13 @@ static int __init lock_torture_init(void)
                 firsterr = -EINVAL;
                 goto unwind;
         }
+
+        if (nwriters_stress == 0 && nreaders_stress == 0) {
+                pr_alert("lock-torture: must run at least one locking thread\n");
+                firsterr = -EINVAL;
+                goto unwind;
+        }
+
         if (cxt.cur_ops->init)
                 cxt.cur_ops->init();
 
@@ -909,17 +915,19 @@ static int __init lock_torture_init(void)
 #endif
 
         /* Initialize the statistics so that each run gets its own numbers. */
+        if (nwriters_stress) {
+                lock_is_write_held = 0;
+                cxt.lwsa = kmalloc(sizeof(*cxt.lwsa) * cxt.nrealwriters_stress, GFP_KERNEL);
+                if (cxt.lwsa == NULL) {
+                        VERBOSE_TOROUT_STRING("cxt.lwsa: Out of memory");
+                        firsterr = -ENOMEM;
+                        goto unwind;
+                }
 
-        lock_is_write_held = 0;
-        cxt.lwsa = kmalloc(sizeof(*cxt.lwsa) * cxt.nrealwriters_stress, GFP_KERNEL);
-        if (cxt.lwsa == NULL) {
-                VERBOSE_TOROUT_STRING("cxt.lwsa: Out of memory");
-                firsterr = -ENOMEM;
-                goto unwind;
-        }
-        for (i = 0; i < cxt.nrealwriters_stress; i++) {
-                cxt.lwsa[i].n_lock_fail = 0;
-                cxt.lwsa[i].n_lock_acquired = 0;
+                for (i = 0; i < cxt.nrealwriters_stress; i++) {
+                        cxt.lwsa[i].n_lock_fail = 0;
+                        cxt.lwsa[i].n_lock_acquired = 0;
+                }
         }
 
         if (cxt.cur_ops->readlock) {
@@ -936,19 +944,21 @@ static int __init lock_torture_init(void)
                         cxt.nrealreaders_stress = cxt.nrealwriters_stress;
                 }
 
-                lock_is_read_held = 0;
-                cxt.lrsa = kmalloc(sizeof(*cxt.lrsa) * cxt.nrealreaders_stress, GFP_KERNEL);
-                if (cxt.lrsa == NULL) {
-                        VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
-                        firsterr = -ENOMEM;
-                        kfree(cxt.lwsa);
-                        cxt.lwsa = NULL;
-                        goto unwind;
-                }
-
-                for (i = 0; i < cxt.nrealreaders_stress; i++) {
-                        cxt.lrsa[i].n_lock_fail = 0;
-                        cxt.lrsa[i].n_lock_acquired = 0;
+                if (nreaders_stress) {
+                        lock_is_read_held = 0;
+                        cxt.lrsa = kmalloc(sizeof(*cxt.lrsa) * cxt.nrealreaders_stress, GFP_KERNEL);
+                        if (cxt.lrsa == NULL) {
+                                VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
+                                firsterr = -ENOMEM;
+                                kfree(cxt.lwsa);
+                                cxt.lwsa = NULL;
+                                goto unwind;
+                        }
+
+                        for (i = 0; i < cxt.nrealreaders_stress; i++) {
+                                cxt.lrsa[i].n_lock_fail = 0;
+                                cxt.lrsa[i].n_lock_acquired = 0;
+                        }
                 }
         }
 
@@ -978,12 +988,14 @@ static int __init lock_torture_init(void)
                         goto unwind;
         }
 
-        writer_tasks = kzalloc(cxt.nrealwriters_stress * sizeof(writer_tasks[0]),
-                               GFP_KERNEL);
-        if (writer_tasks == NULL) {
-                VERBOSE_TOROUT_ERRSTRING("writer_tasks: Out of memory");
-                firsterr = -ENOMEM;
-                goto unwind;
+        if (nwriters_stress) {
+                writer_tasks = kzalloc(cxt.nrealwriters_stress * sizeof(writer_tasks[0]),
+                                       GFP_KERNEL);
+                if (writer_tasks == NULL) {
+                        VERBOSE_TOROUT_ERRSTRING("writer_tasks: Out of memory");
+                        firsterr = -ENOMEM;
+                        goto unwind;
+                }
         }
 
         if (cxt.cur_ops->readlock) {