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  1. 08 Apr, 2008 4 commits
    • Ilpo Järvinen's avatar
      [TCP]: Don't allow FRTO to take place while MTU is being probed · 6adb4f73
      Ilpo Järvinen authored 
      MTU probe can cause some remedies for FRTO because the normal
packet ordering may be violated allowing FRTO to make a wrong
decision (it might not be that serious threat for anything
though). Thus it's safer to not run FRTO while MTU probe is
underway.

It seems that the basic FRTO variant should also look for an
skb at probe_seq.start to check if that's retransmitted one
but I didn't implement it now (plain seqno in window check
isn't robust against wraparounds).
Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      6adb4f73
    • Ilpo Järvinen's avatar
      [TCP]: tcp_simple_retransmit can cause S+L · 882bebaa
      Ilpo Järvinen authored 
      This fixes Bugzilla #10384

tcp_simple_retransmit does L increment without any checking
whatsoever for overflowing S+L when Reno is in use.

The simplest scenario I can currently think of is rather
complex in practice (there might be some more straightforward
cases though). Ie., if mss is reduced during mtu probing, it
may end up marking everything lost and if some duplicate ACKs
arrived prior to that sacked_out will be non-zero as well,
leading to S+L > packets_out, tcp_clean_rtx_queue on the next
cumulative ACK or tcp_fastretrans_alert on the next duplicate
ACK will fix the S counter.

More straightforward (but questionable) solution would be to
just call tcp_reset_reno_sack() in tcp_simple_retransmit but
it would negatively impact the probe's retransmission, ie.,
the retransmissions would not occur if some duplicate ACKs
had arrived.

So I had to add reno sacked_out reseting to CA_Loss state
when the first cumulative ACK arrives (this stale sacked_out
might actually be the explanation for the reports of left_out
overflows in kernel prior to 2.6.23 and S+L overflow reports
of 2.6.24). However, this alone won't be enough to fix kernel
before 2.6.24 because it is building on top of the commit
1b6d427b ([TCP]: Reduce sacked_out with reno when purging
write_queue) to keep the sacked_out from overflowing.
Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Reported-by: default avatarAlessandro Suardi <alessandro.suardi@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      882bebaa
    • Ilpo Järvinen's avatar
      [TCP]: Fix NewReno's fast rexmit/recovery problems with GSOed skb · c137f3dd
      Ilpo Järvinen authored 
      Fixes a long-standing bug which makes NewReno recovery crippled.
With GSO the whole head skb was marked as LOST which is in
violation of NewReno procedure that only wants to mark one packet
and ended up breaking our TCP code by causing counter overflow
because our code was built on top of assumption about valid
NewReno procedure. This manifested as triggering a WARN_ON for
the overflow in a number of places.

It seems relatively safe alternative to just do nothing if
tcp_fragment fails due to oom because another duplicate ACK is
likely to be received soon and the fragmentation will be retried.

Special thanks goes to Soeren Sonnenburg <kernel@nn7.de> who was
lucky enough to be able to reproduce this so that the warning
for the overflow was hit. It's not as easy task as it seems even
if this bug happens quite often because the amount of outstanding
data is pretty significant for the mismarkings to lead to an
overflow.

Because it's very late in 2.6.25-rc cycle (if this even makes in
time), I didn't want to touch anything with SACK enabled here.
Fragmenting might be useful for it as well but it's more or less
a policy decision rather than mandatory fix. Thus there's no need
to rush and we can postpone considering tcp_fragment with SACK
for 2.6.26.

In 2.6.24 and earlier, this very same bug existed but the effect
is slightly different because of a small changes in the if
conditions that fit to the patch's context. With them nothing
got lost marker and thus no retransmissions happened.
Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      c137f3dd
    • Ilpo Järvinen's avatar
      [TCP]: Restore 2.6.24 mark_head_lost behavior for newreno/fack · 1b69d745
      Ilpo Järvinen authored 
      The fast retransmission can be forced locally to the rfc3517
branch in tcp_update_scoreboard instead of making such fragile
constructs deeper in tcp_mark_head_lost.

This is necessary for the next patch which must not have
loopholes for cnt > packets check. As one can notice,
readability got some improvements too because of this :-).
Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      1b69d745
  3. 04 Apr, 2008 6 commits
  5. 03 Apr, 2008 5 commits
  7. 02 Apr, 2008 25 commits