On Fri, Sep 11, 2020 at 06:52:08AM -0700, Paul E. McKenney wrote: > On Fri, Sep 11, 2020 at 03:09:41PM +1000, Alexey Kardashevskiy wrote: > > On 11/09/2020 04:53, Paul E. McKenney wrote: > > > On Wed, Sep 09, 2020 at 10:31:03PM +1000, Alexey Kardashevskiy wrote: [ . . . ] > > >> init_srcu_struct_nodes() assumes ssp->sda!=NULL but alloc_percpu() fails > > >> here: > > >> > > >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/percpu.c#n1734 > > >> === > > >> } else if (mutex_lock_killable(&pcpu_alloc_mutex)) { > > >> pcpu_memcg_post_alloc_hook(objcg, NULL, 0, size); > > >> return NULL; > > >> === > > >> > > >> I am still up to reading that osr-rcuusage.pdf to provide better > > >> analysis :) Thanks, > > > > > > Ah, got it! Does the following patch help? > > > > > > There will likely also need to be changes to cleanup_srcu_struct(), > > > but first let's see if I understand the problem. ;-) > > > > > > Thanx, Paul > > > > > > ------------------------------------------------------------------------ > > > > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > > index c13348e..6f7880a 100644 > > > --- a/kernel/rcu/srcutree.c > > > +++ b/kernel/rcu/srcutree.c > > > @@ -177,11 +177,13 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) > > > INIT_DELAYED_WORK(&ssp->work, process_srcu); > > > if (!is_static) > > > ssp->sda = alloc_percpu(struct srcu_data); > > > + if (!ssp->sda) > > > + return -ENOMEM; > > > init_srcu_struct_nodes(ssp, is_static); > > > ssp->srcu_gp_seq_needed_exp = 0; > > > ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); > > > smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */ > > > > The line above confuses me a bit. What you propose returns without > > smp_store_release() called which should not matter I suppose. > > The idea is that if init_srcu_struct() returns -ENOMEM, the structure > has not been initialized and had better not be used. If the calling code > cannot handle that outcome, then the calling code needs to do something > to insulate init_srcu_struct() from signals. One thing that it could > do would be to invoke init_srcu_struct() from a workqueue handler and > wait for this handler to complete. > > Please keep in mind that there is nothing init_srcu_struct() can do > about this: The srcu_struct is useless unless alloc_percpu() succeeds. > > And yes, I do need to update the header comments to make this clear. > > > Otherwise it should work, although I cannot verify right now as my box > > went down and since it is across Pacific - it may take time to power > > cycle it :) Thanks, > > I know that feeling! And here is hoping that the box is out of reach > of the local hot spots. ;-) Just following up... Did that patch help? Thanx, Paul
