Re: [PATCH] rcu: Use task_state_to_char() in stall-warning prints

["Kunwu Chan" <kunwu.chan@linux.dev>]

June 12, 2026 at 3:58 AM, "Paul E. McKenney" <paulmck@kernel.org mailto:paulmck@kernel.org?to=%22Paul%20E.%20McKenney%22%20%3Cpaulmck%40kernel.org%3E > wrote:


> 
> On Thu, Jun 11, 2026 at 03:32:01PM +0800, Kunwu Chan wrote:
> 
> > 
> > From: Kunwu Chan <kunwu.chan@gmail.com>
> >  
> >  RCU stall warnings currently print task states as raw hexadecimal
> >  values (e.g., ->state=0x402), forcing developers to manually decode
> >  them from memory.
> >  
> >  Replace these raw hex values with the compact, single-letter symbols
> >  already established by sched_show_task():
> >  
> >  ->state=0x402 becomes ->state=I (TASK_IDLE)
> >  ->state=0x0 becomes ->state=R (TASK_RUNNING)
> >  ->state=0x2 becomes ->state=D (TASK_UNINTERRUPTIBLE)
> >  
> >  Convert five print sites across tree_stall.h, rcutorture.c, and
> >  hazptrtorture.c to use task_state_to_char() instead of the raw
> >  ->__state value.
> >  
> >  Suggested-by: Zqiang <qiang.zhang@linux.dev>
> >  Co-developed-by: Wang Lian <lianux.mm@gmail.com>
> >  Signed-off-by: Wang Lian <lianux.mm@gmail.com>
> >  Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
> > 
> Nice!
> 
> But could you please split this into three commits, one for each file?
> That makes it easier to create branches to send to Linus. Especially
> since hazptrtorture.c will likely be in a different pull request. ;-)
> 
>  Thanx, Paul
> 

Sure, I'll split it into one commit per file. 
Makes sense, especially for the hazptr one. ;-)

Thanks!

> > 
> > ---
> >  Based on: linux-rcu repo (dev branch)
> >  URL: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> >  base-commit: 85bf11e84 ("smp: Make CSD lock acquisition atomic for debug mode")
> >  ---
> >  kernel/rcu/hazptrtorture.c | 4 ++--
> >  kernel/rcu/rcutorture.c | 4 ++--
> >  kernel/rcu/tree_stall.h | 12 ++++++------
> >  3 files changed, 10 insertions(+), 10 deletions(-)
> >  
> >  diff --git a/kernel/rcu/hazptrtorture.c b/kernel/rcu/hazptrtorture.c
> >  index 0da0a4606..19ea479c9 100644
> >  --- a/kernel/rcu/hazptrtorture.c
> >  +++ b/kernel/rcu/hazptrtorture.c
> >  @@ -497,10 +497,10 @@ hazptr_torture_stats_print(void)
> >  unsigned long __maybe_unused gp_seq = 0;
> >  
> >  wtp = READ_ONCE(writer_task);
> >  - pr_alert("??? Writer stall state %s(%d) g%lu f%#x ->state %#x cpu %d\n",
> >  + pr_alert("??? Writer stall state %s(%d) g%lu f%#x ->state %c cpu %d\n",
> >  hazptr_torture_writer_state_getname(),
> >  hazptr_torture_writer_state, gp_seq, flags,
> >  - wtp == NULL ? ~0U : wtp->__state,
> >  + wtp == NULL ? '?' : task_state_to_char(wtp),
> >  wtp == NULL ? -1 : (int)task_cpu(wtp));
> >  if (!splatted && wtp) {
> >  sched_show_task(wtp);
> >  diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> >  index fcb421ced..4d4ebeeea 100644
> >  --- a/kernel/rcu/rcutorture.c
> >  +++ b/kernel/rcu/rcutorture.c
> >  @@ -3074,10 +3074,10 @@ rcu_torture_stats_print(void)
> >  if (cur_ops->get_gp_data)
> >  cur_ops->get_gp_data(&flags, &gp_seq);
> >  wtp = READ_ONCE(writer_task);
> >  - pr_alert("??? Writer stall state %s(%d) g%lu f%#x ->state %#x cpu %d\n",
> >  + pr_alert("??? Writer stall state %s(%d) g%lu f%#x ->state %c cpu %d\n",
> >  rcu_torture_writer_state_getname(),
> >  rcu_torture_writer_state, gp_seq, flags,
> >  - wtp == NULL ? ~0U : wtp->__state,
> >  + wtp == NULL ? '?' : task_state_to_char(wtp),
> >  wtp == NULL ? -1 : (int)task_cpu(wtp));
> >  if (!splatted && wtp) {
> >  sched_show_task(wtp);
> >  diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> >  index 317ef91b1..7ca434b08 100644
> >  --- a/kernel/rcu/tree_stall.h
> >  +++ b/kernel/rcu/tree_stall.h
> >  @@ -596,13 +596,13 @@ static void rcu_check_gp_kthread_starvation(void)
> >  
> >  if (rcu_is_gp_kthread_starving(&j)) {
> >  cpu = gpk ? task_cpu(gpk) : -1;
> >  - pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x ->cpu=%d\n",
> >  + pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%c ->cpu=%d\n",
> >  rcu_state.name, j,
> >  (long)rcu_seq_current(&rcu_state.gp_seq),
> >  data_race(READ_ONCE(rcu_state.gp_flags)),
> >  gp_state_getname(rcu_state.gp_state),
> >  data_race(READ_ONCE(rcu_state.gp_state)),
> >  - gpk ? data_race(READ_ONCE(gpk->__state)) : ~0, cpu);
> >  + gpk ? task_state_to_char(gpk) : '?', cpu);
> >  if (gpk) {
> >  struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
> >  
> >  @@ -639,12 +639,12 @@ static void rcu_check_gp_kthread_expired_fqs_timer(void)
> >  time_after(jiffies, jiffies_fqs + RCU_STALL_MIGHT_MIN) &&
> >  gpk && !READ_ONCE(gpk->on_rq)) {
> >  cpu = task_cpu(gpk);
> >  - pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x\n",
> >  + pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%c\n",
> >  rcu_state.name, (jiffies - jiffies_fqs),
> >  (long)rcu_seq_current(&rcu_state.gp_seq),
> >  data_race(READ_ONCE(rcu_state.gp_flags)), // Diagnostic read
> >  gp_state_getname(RCU_GP_WAIT_FQS), RCU_GP_WAIT_FQS,
> >  - data_race(READ_ONCE(gpk->__state)));
> >  + task_state_to_char(gpk));
> >  pr_err("\tPossible timer handling issue on cpu=%d timer-softirq=%u\n",
> >  cpu, kstat_softirqs_cpu(TIMER_SOFTIRQ, cpu));
> >  }
> >  @@ -971,10 +971,10 @@ void show_rcu_gp_kthreads(void)
> >  jr = j - data_race(READ_ONCE(rcu_state.gp_req_activity));
> >  js = j - data_race(READ_ONCE(rcu_state.gp_start));
> >  jw = j - data_race(READ_ONCE(rcu_state.gp_wake_time));
> >  - pr_info("%s: wait state: %s(%d) ->state: %#x ->rt_priority %u delta ->gp_start %lu ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_max %lu ->gp_flags %#x\n",
> >  + pr_info("%s: wait state: %s(%d) ->state: %c ->rt_priority %u delta ->gp_start %lu ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_max %lu ->gp_flags %#x\n",
> >  rcu_state.name, gp_state_getname(rcu_state.gp_state),
> >  data_race(READ_ONCE(rcu_state.gp_state)),
> >  - t ? data_race(READ_ONCE(t->__state)) : 0x1ffff, t ? t->rt_priority : 0xffU,
> >  + t ? task_state_to_char(t) : '?', t ? t->rt_priority : 0xffU,
> >  js, ja, jr, jw, (long)data_race(READ_ONCE(rcu_state.gp_wake_seq)),
> >  (long)data_race(READ_ONCE(rcu_state.gp_seq)),
> >  (long)data_race(READ_ONCE(rcu_get_root()->gp_seq_needed)),
> >  -- 
> >  2.43.0
> >
>