On Sat, Aug 25, 2012 at 11:36:23AM +0800, Fengguang Wu wrote:
> Greetings,
>
> I got this warning on 3.6.0-rc2. Full dmesg/config attached.
>
> [ 3.051375] Initializing RT-Tester: OK
> [ 3.052491] rcu-torture:--- Start of test: nreaders=2 nfakewriters=4
> stat_interval=0 verbose=0 test_no_idle_hz=0 shuffle_interval=3 stut
> ter=5 irqreader=1 fqs_duration=0 fqs_holdoff=0 fqs_stutter=3 test_boost=1/1
> test_boost_interval=7 test_boost_duration=4 shutdown_secs=0 onoff_interval=0
> onoff_holdoff=0
> [ 3.059084]
> [ 3.059451] ===============================
> [ 3.060454] [ INFO: suspicious RCU usage. ]
> [ 3.061482] 3.6.0-rc2-00010-g4c58c42 #59 Not tainted
> [ 3.062686] -------------------------------
> [ 3.063744] /c/kernel-tests/src/stable/kernel/rcutorture.c:990 suspicious
> rcu_dereference_check() usage!
>
> 982 do {
> 983 schedule_timeout_uninterruptible(1);
> 984 rp = rcu_torture_alloc();
> 985 if (rp == NULL)
> 986 continue;
> 987 rp->rtort_pipe_count = 0;
> 988 udelay(rcu_random(&rand) & 0x3ff);
> 989 old_rp = rcu_dereference_check(rcu_torture_current,
> >990 current == writer_task);
> 991 rp->rtort_mbtest = 1;
> 992 rcu_assign_pointer(rcu_torture_current, rp);
> 993 smp_wmb(); /* Mods to old_rp must follow
> rcu_assign_pointer() */
> 994 if (old_rp) {
Does the following clear this up?
Thanx, Paul
------------------------------------------------------------------------
rcu: Prevent initialization race in rcutorture kthreads
When you do something like "t = kthread_run(...)", it is possible that
the kthread will start running before the assignment to "t" happens.
If the child kthread expects to find a pointer to its task_struct in "t",
it will then be fatally disappointed. This commit therefore switches
such cases to kthread_create() followed by wake_up_process(), guaranteeing
that the assignment happens before the child kthread starts running.
Reported-by: Fengguang Wu <fengguang...@intel.com>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 7a97b5b..8ff4fad 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -2028,14 +2028,15 @@ rcu_torture_init(void)
/* Start up the kthreads. */
VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task");
- writer_task = kthread_run(rcu_torture_writer, NULL,
- "rcu_torture_writer");
+ writer_task = kthread_create(rcu_torture_writer, NULL,
+ "rcu_torture_writer");
if (IS_ERR(writer_task)) {
firsterr = PTR_ERR(writer_task);
VERBOSE_PRINTK_ERRSTRING("Failed to create writer");
writer_task = NULL;
goto unwind;
}
+ wake_up_process(writer_task);
fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]),
GFP_KERNEL);
if (fakewriter_tasks == NULL) {
@@ -2150,14 +2151,15 @@ rcu_torture_init(void)
}
if (shutdown_secs > 0) {
shutdown_time = jiffies + shutdown_secs * HZ;
- shutdown_task = kthread_run(rcu_torture_shutdown, NULL,
- "rcu_torture_shutdown");
+ shutdown_task = kthread_create(rcu_torture_shutdown, NULL,
+ "rcu_torture_shutdown");
if (IS_ERR(shutdown_task)) {
firsterr = PTR_ERR(shutdown_task);
VERBOSE_PRINTK_ERRSTRING("Failed to create shutdown");
shutdown_task = NULL;
goto unwind;
}
+ wake_up_process(shutdown_task);
}
i = rcu_torture_onoff_init();
if (i != 0) {
--
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