On Mon, Aug 16, 2021 at 10:02:28PM +0000, David Chen wrote: > > > > -----Original Message----- > > From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > Sent: Monday, August 16, 2021 12:31 PM > > To: David Chen <david.chen@xxxxxxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx; Paul E. McKenney > > <paulmck@xxxxxxxxxxxxxxxxxx>; neeraju@xxxxxxxxxxxxxx > > Subject: Re: Request for backport fd6bc19d7676 to 4.14 and 4.19 branch > > > > On Mon, Aug 16, 2021 at 07:19:34PM +0000, David Chen wrote: > > > Hi Greg, > > > > > > We recently hit a hung task timeout issue in synchronize_rcu_expedited on > > 4.14 branch. > > > The issue seems to be identical to the one described in `fd6bc19d7676 > > > rcu: Fix missed wakeup of exp_wq waiters` Can we backport it to 4.14 and > > 4.19 branch? > > > The patch doesn't apply cleanly, but it should be trivial to resolve, > > > just do this > > > > > > - wake_up_all(&rnp->exp_wq[rcu_seq_ctr(rsp- > > >expedited_sequence) & 0x3]); > > > + wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]); > > > > > > I don't know if we should do it for 4.9, because the handling of sequence > > number is a bit different. > > > > Please provide a working backport, me hand-editing patches does not scale, > > and this way you get the proper credit for backporting it (after testing it). > > Sure, appended at the end. > > > > > You have tested, this, right? > > I don't have a good repro for the original issue, so I only ran rcutorture and > some basic work load test to see if anything obvious went wrong. Ideally you would be able to also hit this without the patch on the older kernels, is this the case? thanks, greg k-h
