On 2022/8/2 7:14, Paul E. McKenney wrote: > On Sat, Jul 30, 2022 at 06:23:28PM +0800, Zhen Lei wrote: >> The backtrace of cpu_curr(other_cpu) is unwinded based on the 'fp' saved >> during its last switch-out. For the most part, it's out of date. So try >> to use NMI to get the backtrace first, just like those functions in >> "tree_stall.h" did. Such as rcu_dump_cpu_stacks(). >> >> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx> > > Much better, thank you! > >> --- >> kernel/rcu/tree_exp.h | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h >> index 0f70f62039a9090..21381697de23f0b 100644 >> --- a/kernel/rcu/tree_exp.h >> +++ b/kernel/rcu/tree_exp.h >> @@ -665,7 +665,8 @@ static void synchronize_rcu_expedited_wait(void) >> mask = leaf_node_cpu_bit(rnp, cpu); >> if (!(READ_ONCE(rnp->expmask) & mask)) >> continue; >> - dump_cpu_task(cpu); >> + if (!trigger_single_cpu_backtrace(cpu)) >> + dump_cpu_task(cpu); > > But why not just leave this unchanged, rather than adding the call to > trigger_single_cpu_backtrace() in this patch and then removing it in > the next patch? To make the patch clear and easy to describe. Otherwise, I need to give an additional description of it in the next patch, because I searched all dump_cpu_task(). This seems to make the next patch less simple. Some of the patch sets I've seen have been done step by step like this. But I can't find it now. On the other hand, this patch is a small fix. Earlier versions may only backport it, not the next cleanup patch. > > Thanx, Paul > >> } >> } >> jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3; >> -- >> 2.25.1 >> > . > -- Regards, Zhen Lei
