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Message-ID: <20211110174453.3cb33cde@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Date: Wed, 10 Nov 2021 17:44:53 -0800 From: Jakub Kicinski <kuba@...nel.org> To: Alexander Lobakin <alexandr.lobakin@...el.com> Cc: Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, Jesse Brandeburg <jesse.brandeburg@...el.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Michal Swiatkowski <michal.swiatkowski@...el.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Antoine Tenart <atenart@...nel.org>, Wei Wang <weiwan@...gle.com>, Björn Töpel <bjorn@...nel.org>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net] net: fix premature exit from NAPI state polling in napi_disable() On Wed, 10 Nov 2021 17:44:07 -0800 Jakub Kicinski wrote: > On Wed, 10 Nov 2021 20:43:37 +0100 Alexander Lobakin wrote: > > > What about replacing the error prone do {...} while (cmpxchg(..)) by > > > something less confusing ? > > > > > > This way, no need for a label. > > > > > > diff --git a/net/core/dev.c b/net/core/dev.c > > > index 5e37d6809317fb3c54686188a908bfcb0bfccdab..9327141892cdaaf0282e082e0c6746abae0f12a7 > > > 100644 > > > --- a/net/core/dev.c > > > +++ b/net/core/dev.c > > > @@ -6264,7 +6264,7 @@ void napi_disable(struct napi_struct *n) > > > might_sleep(); > > > set_bit(NAPI_STATE_DISABLE, &n->state); > > > > > > - do { > > > + for (;;) { > > > val = READ_ONCE(n->state); > > > if (val & (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC)) { > > > usleep_range(20, 200); > > > @@ -6273,7 +6273,9 @@ void napi_disable(struct napi_struct *n) > > > > > > new = val | NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC; > > > new &= ~(NAPIF_STATE_THREADED | NAPIF_STATE_PREFER_BUSY_POLL); > > > - } while (cmpxchg(&n->state, val, new) != val); > > > + if (cmpxchg(&n->state, val, new) == val) > > > + break; > > > + } > > > > > > hrtimer_cancel(&n->timer); > > > > LFTM, I'l queue v2 in a moment with you in Suggested-by. > > Ouch. > > Feel free to put > > Acked-by: Jakub Kicinski <kuba@...nel.org> Or I'll do it myself since it's already out...
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