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 For the most part, it's out of date.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. Thanx, Paul > >> } > >> } > >> jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3; > >> -- > >> 2.25.1 > >> > > . > > > > -- > Regards, > Zhen Lei
