Messages in this thread | | | Date | Fri, 2 Apr 2021 12:02:21 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 3/3] srcu: Fix broken node geometry after early ssp init |
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On Thu, Apr 01, 2021 at 06:12:41PM -0700, Paul E. McKenney wrote: > On Fri, Apr 02, 2021 at 01:47:04AM +0200, Frederic Weisbecker wrote: gg> > void __init srcu_init(void) > > { > > - struct srcu_struct *ssp; > > + static struct srcu_data __initdata old_sdp; > > + static struct srcu_node __initdata old_mynode; > > + struct srcu_struct *ssp, *tmp; > > > > srcu_init_done = true; > > - while (!list_empty(&srcu_boot_list)) { > > - ssp = list_first_entry(&srcu_boot_list, struct srcu_struct, > > - work.work.entry); > > + /* > > + * ssp's that got initialized before rcu_init_geometry() have a stale > > + * node hierarchy. Rebuild their node trees and propagate states from > > + * pruned leaf nodes. > > + */ > > + list_for_each_entry_safe(ssp, tmp, &srcu_early_init_list, early_init) { > > + struct srcu_data *sdp = this_cpu_ptr(ssp->sda); > > + > > + list_del(&ssp->early_init); > > + old_sdp = *sdp; > > + old_mynode = *sdp->mynode; > > + init_srcu_struct_nodes(ssp); > > + restore_srcu_sdp(sdp, &old_sdp, &old_mynode); > > Why not just pull all of the pre-initialization callbacks onto a local > list (re-initialization the rcu_segcblist structures if necessary), > then iterate through that list re-invoking call_srcu() on each? > There shouldn't be that many pre-initialization call_srcu() invocations, > and if someday there are, it would not be hard to make __call_srcu() > take lists of callbacks and a count instead of a single callback, correct? > > Or am I once again missing something basic?
So that would work for callbacks based started grace periods but not for the others. So if anybody calls start_poll_synchronize_rcu() early, simply requeuing the callbacks won't help. Even worse, a blind reinitialization of the ssp would lose the started grace period and a future poll_state_synchronize_rcu() might never succeed.
Arguably that's a quite a corner case and I don't expect anyone to call start_poll_synchronize_srcu() so early but who knows. An alternative is to forbid it and warn if used before srcu is initialized.
Thanks.
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