On 2022/8/4 8:07, Paul E. McKenney wrote: > On Tue, Aug 02, 2022 at 10:06:00AM +0800, Leizhen (ThunderTown) wrote: >> >> >> 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 For the most part, it's out of date.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. > > You do have the option of doing a Cc to stable to control the backporting, > if that is a potential issue for you. > > On the commit log, just say that the one use case already avoided doing > the trigger_single_cpu_backtrace(), and thus did not need to be updated. > > So please resend the series, but without the undo/redo. There would > thus be two patches rather than three, but there are plenty of other > things that need fixing anyway. OK, thanks. > > Thanx, Paul > >>>> } >>>> } >>>> jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3; >>>> -- >>>> 2.25.1 >>>> >>> . >>> >> >> -- >> Regards, >> Zhen Lei > . > -- Regards, Zhen Lei
