| Message ID | alpine.DEB.2.00.1302041327210.4561@wel-95.cs.helsinki.fi |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Mon, 2013-02-04 at 14:14 +0200, Ilpo Järvinen wrote: > On Sun, 3 Feb 2013, Eric Dumazet wrote: > > > From: Eric Dumazet <edumazet@google.com> > > > > Commit 9dc274151a548 (tcp: fix ABC in tcp_slow_start()) > > uncovered a bug in FRTO code : > > tcp_process_frto() is setting snd_cwnd to 0 if the number > > of in flight packets is 0. > > > > As Neal pointed out, if no packet is in flight we lost our > > chance to disambiguate whether a loss timeout was spurious. > > > > We should assume it was a proper loss. > > > > Reported-by: Pasi Kärkkäinen <pasik@iki.fi> > > Signed-off-by: Neal Cardwell <ncardwell@google.com> > > Signed-off-by: Eric Dumazet <edumazet@google.com> > > Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> > > Cc: Yuchung Cheng <ycheng@google.com> > > --- > > net/ipv4/tcp_input.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > > index 8aca4ee..680c422 100644 > > --- a/net/ipv4/tcp_input.c > > +++ b/net/ipv4/tcp_input.c > > @@ -3484,7 +3484,8 @@ static bool tcp_process_frto(struct sock *sk, int flag) > > ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED))) > > tp->undo_marker = 0; > > > > - if (!before(tp->snd_una, tp->frto_highmark)) { > > + if (!before(tp->snd_una, tp->frto_highmark) || > > + !tcp_packets_in_flight(tp)) { > > I think this condition becomes now too broad because there is transient > during FRTO. I think the patch below would be enough to resolve this, > what do you think? > > -- > [PATCH 1/1] tcp: fix for zero packets_in_flight was too broad > > There are transients during normal FRTO procedure during which > the packets_in_flight can go to zero between write_queue state > updates and firing the resulting segments out. As FRTO processing > occurs during that window the check must be more precise to > not match "spuriously" :-). More specificly, e.g., when > packets_in_flight is zero but FLAG_DATA_ACKED is true the problematic > branch that set cwnd into zero would not be taken and new segments > might be sent out later. > > Only compile tested. > > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> > Cc: Neal Cardwell <ncardwell@google.com> > Cc: Eric Dumazet <eric.dumazet@gmail.com> > Cc: Pasi Kärkkäinen <pasik@iki.fi> > --- > net/ipv4/tcp_input.c | 8 ++++++-- > 1 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > index 680c422..500c2da 100644 > --- a/net/ipv4/tcp_input.c > +++ b/net/ipv4/tcp_input.c > @@ -3484,8 +3484,7 @@ static bool tcp_process_frto(struct sock *sk, int flag) > ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED))) > tp->undo_marker = 0; > > - if (!before(tp->snd_una, tp->frto_highmark) || > - !tcp_packets_in_flight(tp)) { > + if (!before(tp->snd_una, tp->frto_highmark)) { > tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag); > return true; > } > @@ -3505,6 +3504,11 @@ static bool tcp_process_frto(struct sock *sk, int flag) > } > } else { > if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) { > + if (!tcp_packets_in_flight(tp)) { > + tcp_enter_frto_loss(sk, 2, flag); > + return true; > + } > + > /* Prevent sending of new data. */ > tp->snd_cwnd = min(tp->snd_cwnd, > tcp_packets_in_flight(tp)); Thanks Ilpo. I'll be able to test your patch under load only in ~8 hours. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, 2013-02-04 at 07:07 -0800, Eric Dumazet wrote: > Thanks Ilpo. > > I'll be able to test your patch under load only in ~8 hours. Sorry for the delay. The patch survived my tests ;) Tested-by: Eric Dumazet <edumazet@google.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Feb 4, 2013 at 7:14 AM, Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> wrote: > [PATCH 1/1] tcp: fix for zero packets_in_flight was too broad > > There are transients during normal FRTO procedure during which > the packets_in_flight can go to zero between write_queue state > updates and firing the resulting segments out. As FRTO processing > occurs during that window the check must be more precise to > not match "spuriously" :-). More specificly, e.g., when > packets_in_flight is zero but FLAG_DATA_ACKED is true the problematic > branch that set cwnd into zero would not be taken and new segments > might be sent out later. > > Only compile tested. > > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> > Cc: Neal Cardwell <ncardwell@google.com> > Cc: Eric Dumazet <eric.dumazet@gmail.com> > Cc: Pasi Kärkkäinen <pasik@iki.fi> > --- > net/ipv4/tcp_input.c | 8 ++++++-- > 1 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > index 680c422..500c2da 100644 > --- a/net/ipv4/tcp_input.c > +++ b/net/ipv4/tcp_input.c > @@ -3484,8 +3484,7 @@ static bool tcp_process_frto(struct sock *sk, int flag) > ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED))) > tp->undo_marker = 0; > > - if (!before(tp->snd_una, tp->frto_highmark) || > - !tcp_packets_in_flight(tp)) { > + if (!before(tp->snd_una, tp->frto_highmark)) { > tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag); > return true; > } > @@ -3505,6 +3504,11 @@ static bool tcp_process_frto(struct sock *sk, int flag) > } > } else { > if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) { > + if (!tcp_packets_in_flight(tp)) { > + tcp_enter_frto_loss(sk, 2, flag); > + return true; > + } > + > /* Prevent sending of new data. */ > tp->snd_cwnd = min(tp->snd_cwnd, > tcp_packets_in_flight(tp)); > -- Acked-by: Neal Cardwell <ncardwell@google.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Neal Cardwell <ncardwell@google.com> Date: Tue, 5 Feb 2013 14:49:04 -0500 > On Mon, Feb 4, 2013 at 7:14 AM, Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> wrote: >> [PATCH 1/1] tcp: fix for zero packets_in_flight was too broad >> >> There are transients during normal FRTO procedure during which >> the packets_in_flight can go to zero between write_queue state >> updates and firing the resulting segments out. As FRTO processing >> occurs during that window the check must be more precise to >> not match "spuriously" :-). More specificly, e.g., when >> packets_in_flight is zero but FLAG_DATA_ACKED is true the problematic >> branch that set cwnd into zero would not be taken and new segments >> might be sent out later. >> >> Only compile tested. >> >> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> ... > Acked-by: Neal Cardwell <ncardwell@google.com> Applied, thanks everyone. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Feb 06, 2013 at 03:55:04PM -0500, David Miller wrote: > From: Neal Cardwell <ncardwell@google.com> > Date: Tue, 5 Feb 2013 14:49:04 -0500 > > > On Mon, Feb 4, 2013 at 7:14 AM, Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> wrote: > >> [PATCH 1/1] tcp: fix for zero packets_in_flight was too broad > >> > >> There are transients during normal FRTO procedure during which > >> the packets_in_flight can go to zero between write_queue state > >> updates and firing the resulting segments out. As FRTO processing > >> occurs during that window the check must be more precise to > >> not match "spuriously" :-). More specificly, e.g., when > >> packets_in_flight is zero but FLAG_DATA_ACKED is true the problematic > >> branch that set cwnd into zero would not be taken and new segments > >> might be sent out later. > >> > >> Only compile tested. > >> > >> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> > ... > > Acked-by: Neal Cardwell <ncardwell@google.com> > > Applied, thanks everyone. > Hmm.. are we missing CC stable@kernel.org in these patches? I guess 3.6.x is already EOL, but it'd be nice to get this bug fixed also in 3.7.x .. Thanks, -- Pasi -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Pasi Kärkkäinen <pasik@iki.fi> Date: Wed, 6 Feb 2013 23:13:43 +0200 > On Wed, Feb 06, 2013 at 03:55:04PM -0500, David Miller wrote: >> From: Neal Cardwell <ncardwell@google.com> >> Date: Tue, 5 Feb 2013 14:49:04 -0500 >> >> > On Mon, Feb 4, 2013 at 7:14 AM, Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> wrote: >> >> [PATCH 1/1] tcp: fix for zero packets_in_flight was too broad >> >> >> >> There are transients during normal FRTO procedure during which >> >> the packets_in_flight can go to zero between write_queue state >> >> updates and firing the resulting segments out. As FRTO processing >> >> occurs during that window the check must be more precise to >> >> not match "spuriously" :-). More specificly, e.g., when >> >> packets_in_flight is zero but FLAG_DATA_ACKED is true the problematic >> >> branch that set cwnd into zero would not be taken and new segments >> >> might be sent out later. >> >> >> >> Only compile tested. >> >> >> >> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> >> ... >> > Acked-by: Neal Cardwell <ncardwell@google.com> >> >> Applied, thanks everyone. >> > > Hmm.. are we missing CC stable@kernel.org in these patches? > I guess 3.6.x is already EOL, but it'd be nice to get this bug fixed also in 3.7.x .. We never CC: stable on networking patches, I queue them up manually and submit them at a time of my own choosing. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Feb 06, 2013 at 04:19:19PM -0500, David Miller wrote: > From: Pasi Kärkkäinen <pasik@iki.fi> > Date: Wed, 6 Feb 2013 23:13:43 +0200 > > > On Wed, Feb 06, 2013 at 03:55:04PM -0500, David Miller wrote: > >> From: Neal Cardwell <ncardwell@google.com> > >> Date: Tue, 5 Feb 2013 14:49:04 -0500 > >> > >> > On Mon, Feb 4, 2013 at 7:14 AM, Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> wrote: > >> >> [PATCH 1/1] tcp: fix for zero packets_in_flight was too broad > >> >> > >> >> There are transients during normal FRTO procedure during which > >> >> the packets_in_flight can go to zero between write_queue state > >> >> updates and firing the resulting segments out. As FRTO processing > >> >> occurs during that window the check must be more precise to > >> >> not match "spuriously" :-). More specificly, e.g., when > >> >> packets_in_flight is zero but FLAG_DATA_ACKED is true the problematic > >> >> branch that set cwnd into zero would not be taken and new segments > >> >> might be sent out later. > >> >> > >> >> Only compile tested. > >> >> > >> >> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> > >> ... > >> > Acked-by: Neal Cardwell <ncardwell@google.com> > >> > >> Applied, thanks everyone. > >> > > > > Hmm.. are we missing CC stable@kernel.org in these patches? > > I guess 3.6.x is already EOL, but it'd be nice to get this bug fixed also in 3.7.x .. > > We never CC: stable on networking patches, I queue them up manually > and submit them at a time of my own choosing. > OK, I didn't know that. Thanks :) -- Pasi -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 680c422..500c2da 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -3484,8 +3484,7 @@ static bool tcp_process_frto(struct sock *sk, int flag) ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED))) tp->undo_marker = 0; - if (!before(tp->snd_una, tp->frto_highmark) || - !tcp_packets_in_flight(tp)) { + if (!before(tp->snd_una, tp->frto_highmark)) { tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag); return true; } @@ -3505,6 +3504,11 @@ static bool tcp_process_frto(struct sock *sk, int flag) } } else { if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) { + if (!tcp_packets_in_flight(tp)) { + tcp_enter_frto_loss(sk, 2, flag); + return true; + } + /* Prevent sending of new data. */ tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp));