diff options
| author | Paul E. McKenney <paulmck@kernel.org> | 2025-05-08 16:45:01 -0700 |
|---|---|---|
| committer | Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org> | 2025-06-25 08:39:01 +0530 |
| commit | 635bdb9d22796fc6ba1958ec73ab0a0a693c58d6 (patch) | |
| tree | 5df85864874a99c70c52f3ee6d171da4d11b13e1 | |
| parent | 9ea40db969115022335a553b4f6fe731dcd90c2a (diff) | |
rcutorture: Start rcu_torture_writer() after rcu_torture_reader()
Testing of rcutorture's SRCU-P scenario on a large arm64 system resulted
in rcu_torture_writer() forward-progress failures, but these same tests
passed on x86. After some off-list discussion of possible memory-ordering
causes for these failures, Boqun showed that these were in fact due to
reordering, but by the scheduler, not by the memory system. On x86,
rcu_torture_writer() would have run quickly enough that by the time
the rcu_torture_updown() kthread started, the rcu_torture_current
variable would already be initialized, thus avoiding a bug in which
a NULL value would cause rcu_torture_updown() to do an extra call to
srcu_up_read_fast().
This commit therefore moves creation of the rcu_torture_writer() kthread
after that of the rcu_torture_reader() kthreads. This results in
deterministic failures on x86.
What about the double-srcu_up_read_fast() bug? Boqun has the fix.
But let's also fix the test while we are at it!
Reported-by: Joel Fernandes <joelagnelf@nvidia.com>
Reported-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org>
| -rw-r--r-- | kernel/rcu/rcutorture.c | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index d1e0d61d8815..a209d2419cfd 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -4246,11 +4246,6 @@ rcu_torture_init(void) /* Start up the kthreads. */ rcu_torture_write_types(); - firsterr = torture_create_kthread(rcu_torture_writer, NULL, - writer_task); - if (torture_init_error(firsterr)) - goto unwind; - if (nrealfakewriters > 0) { fakewriter_tasks = kcalloc(nrealfakewriters, sizeof(fakewriter_tasks[0]), @@ -4283,6 +4278,12 @@ rcu_torture_init(void) if (torture_init_error(firsterr)) goto unwind; } + + firsterr = torture_create_kthread(rcu_torture_writer, NULL, + writer_task); + if (torture_init_error(firsterr)) + goto unwind; + nrealnocbers = nocbs_nthreads; if (WARN_ON(nrealnocbers < 0)) nrealnocbers = 1; |