On Tue, Oct 12, 2021 at 03:48:28PM +1100, Stephen Rothwell wrote:
> Hi all,
>
> Today's linux-next merge of the rcu tree got a conflict in:
>
> kernel/rcu/tasks.h
>
> between commit:
>
> 9b3c4ab3045e ("sched,rcu: Rework try_invoke_on_locked_down_task()")
>
> from the tip tree and commit:
>
> 18f08e758f34 ("rcu-tasks: Add trc_inspect_reader() checks for exiting critical section")
>
> from the rcu tree.
>
> I fixed it up (I hope - see below) and can carry the fix as
> necessary. This is now fixed as far as linux-next is concerned, but any
> non trivial conflicts should be mentioned to your upstream maintainer
> when your tree is submitted for merging. You may also want to consider
> cooperating with the maintainer of the conflicting tree to minimise any
> particularly complex conflicts.
Thank you for catching this! I have it down for my upcoming pull
request.
Thanx, Paul
> --
> Cheers,
> Stephen Rothwell
>
> diff --cc kernel/rcu/tasks.h
> index 171bc848e8e3,e4a32db9f712..000000000000
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@@ -928,10 -919,10 +919,10 @@@ reset_ipi
> }
>
> /* Callback function for scheduler to check locked-down task. */
> -static bool trc_inspect_reader(struct task_struct *t, void *arg)
> +static int trc_inspect_reader(struct task_struct *t, void *arg)
> {
> int cpu = task_cpu(t);
> - bool in_qs = false;
> + int nesting;
> bool ofl = cpu_is_offline(cpu);
>
> if (task_curr(t)) {
> @@@ -951,18 -942,18 +942,18 @@@
> n_heavy_reader_updates++;
> if (ofl)
> n_heavy_reader_ofl_updates++;
> - in_qs = true;
> + nesting = 0;
> } else {
> // The task is not running, so C-language access is safe.
> - in_qs = likely(!t->trc_reader_nesting);
> + nesting = t->trc_reader_nesting;
> }
>
> - // Mark as checked so that the grace-period kthread will
> - // remove it from the holdout list.
> - t->trc_reader_checked = true;
> -
> - if (in_qs)
> - return 0; // Already in quiescent state, done!!!
> + // If not exiting a read-side critical section, mark as checked
> + // so that the grace-period kthread will remove it from the
> + // holdout list.
> + t->trc_reader_checked = nesting >= 0;
> + if (nesting <= 0)
> - return !nesting; // If in QS, done, otherwise try again later.
> ++ return (!nesting) ? 0 : -EINVAL; // If in QS, done, otherwise try again later.
>
> // The task is in a read-side critical section, so set up its
> // state so that it will awaken the grace-period kthread upon exit
