Le Mon, Apr 28, 2025 at 05:54:03PM +0800, Zqiang a écrit : > For Preempt-RT kernel, when enable CONFIG_PROVE_RCU Kconfig, > disable local bh in rcuc kthreads will not affect preempt_count(), > this resulted in the following splat: > > WARNING: suspicious RCU usage > kernel/rcu/tree_plugin.h:36 Unsafe read of RCU_NOCB offloaded state! > stack backtrace: > CPU: 0 UID: 0 PID: 22 Comm: rcuc/0 > Call Trace: > [ 0.407907] <TASK> > [ 0.407910] dump_stack_lvl+0xbb/0xd0 > [ 0.407917] dump_stack+0x14/0x20 > [ 0.407920] lockdep_rcu_suspicious+0x133/0x210 > [ 0.407932] rcu_rdp_is_offloaded+0x1c3/0x270 > [ 0.407939] rcu_core+0x471/0x900 > [ 0.407942] ? lockdep_hardirqs_on+0xd5/0x160 > [ 0.407954] rcu_cpu_kthread+0x25f/0x870 > [ 0.407959] ? __pfx_rcu_cpu_kthread+0x10/0x10 > [ 0.407966] smpboot_thread_fn+0x34c/0xa50 > [ 0.407970] ? trace_preempt_on+0x54/0x120 > [ 0.407977] ? __pfx_smpboot_thread_fn+0x10/0x10 > [ 0.407982] kthread+0x40e/0x840 > [ 0.407990] ? __pfx_kthread+0x10/0x10 > [ 0.407994] ? rt_spin_unlock+0x4e/0xb0 > [ 0.407997] ? rt_spin_unlock+0x4e/0xb0 > [ 0.408000] ? __pfx_kthread+0x10/0x10 > [ 0.408006] ? __pfx_kthread+0x10/0x10 > [ 0.408011] ret_from_fork+0x40/0x70 > [ 0.408013] ? __pfx_kthread+0x10/0x10 > [ 0.408018] ret_from_fork_asm+0x1a/0x30 > [ 0.408042] </TASK> > > Currently, triggering an rdp offloaded state change need the > corresponding rdp's CPU goes offline, and at this time the rcuc > kthreads has already in parking state. this means the corresponding > rcuc kthreads can safely read offloaded state of rdp while it's > corresponding cpu is online. > > This commit therefore add rdp->rcu_cpu_kthread_task check for > Preempt-RT kernels. > > Signed-off-by: Zqiang <qiang.zhang1...@gmail.com> > --- > kernel/rcu/tree_plugin.h | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 003e549f6514..fe728eded36e 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -31,7 +31,9 @@ static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) > lockdep_is_held(&rcu_state.nocb_mutex) || > (!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible()) && > rdp == this_cpu_ptr(&rcu_data)) || > - rcu_current_is_nocb_kthread(rdp)), > + rcu_current_is_nocb_kthread(rdp) || > + (IS_ENABLED(CONFIG_PREEMPT_RT) && > + current == rdp->rcu_cpu_kthread_task)),
Isn't it safe also on !CONFIG_PREEMPT_RT ? Thanks. > "Unsafe read of RCU_NOCB offloaded state" > ); > > -- > 2.17.1 > -- Frederic Weisbecker SUSE Labs
