From: Zqiang qiang1.zhang@intel.com
[ Upstream commit 92366810644d5675043c792abb70eaf974a77384 ]
Systems built with CONFIG_DEBUG_PREEMPT=y can trigger the following BUG while running the rcuscale performance test:
BUG: using smp_processor_id() in preemptible [00000000] code: rcu_scale_write/69 CPU: 0 PID: 66 Comm: rcu_scale_write Not tainted 5.18.0-rc7-next-20220517-yoctodev-standard+ caller is debug_smp_processor_id+0x17/0x20 Call Trace: <TASK> dump_stack_lvl+0x49/0x5e dump_stack+0x10/0x12 check_preemption_disabled+0xdf/0xf0 debug_smp_processor_id+0x17/0x20 rcu_scale_writer+0x2b5/0x580 kthread+0x177/0x1b0 ret_from_fork+0x22/0x30 </TASK>
Reproduction method: runqemu kvm slirp nographic qemuparams="-m 4096 -smp 8" bootparams="isolcpus=2,3 nohz_full=2,3 rcu_nocbs=2,3 rcutree.dump_tree=1 rcuscale.shutdown=false rcuscale.gp_async=true" -d
The problem is that the rcu_scale_writer() kthreads fail to set the PF_NO_SETAFFINITY flags, which causes is_percpu_thread() to assume that the kthread's affinity might change at any time, thus the BUG noted above.
This commit therefore causes rcu_scale_writer() to set PF_NO_SETAFFINITY in its kthread's ->flags field, thus preventing this BUG.
Signed-off-by: Zqiang qiang1.zhang@intel.com Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/rcu/rcuscale.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c index 2cc34a22a506..525b1687ab3e 100644 --- a/kernel/rcu/rcuscale.c +++ b/kernel/rcu/rcuscale.c @@ -399,6 +399,7 @@ rcu_scale_writer(void *arg) VERBOSE_SCALEOUT_STRING("rcu_scale_writer task started"); WARN_ON(!wdpp); set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids)); + current->flags |= PF_NO_SETAFFINITY; sched_set_fifo_low(current);
if (holdoff)