linux-toradex.git/net/ipv4/tcp_input.c, branch v3.0.29

tcp: fix tcp_shift_skb_data() to not shift SACKed data below snd_una

2012-03-19T15:57:46+00:00

[ Upstream commit 4648dc97af9d496218a05353b0e442b3dfa6aaab ]

This commit fixes tcp_shift_skb_data() so that it does not shift
SACKed data below snd_una.

This fixes an issue whose symptoms exactly match reports showing
tp->sacked_out going negative since 3.3.0-rc4 (see "WARNING: at
net/ipv4/tcp_input.c:3418" thread on netdev).

Since 2008 (832d11c5cd076abc0aa1eaf7be96c81d1a59ce41)
tcp_shift_skb_data() had been shifting SACKed ranges that were below
snd_una. It checked that the *end* of the skb it was about to shift
from was above snd_una, but did not check that the end of the actual
shifted range was above snd_una; this commit adds that check.

Shifting SACKed ranges below snd_una is problematic because for such
ranges tcp_sacktag_one() short-circuits: it does not declare anything
as SACKed and does not increase sacked_out.

Before the fixes in commits cc9a672ee522d4805495b98680f4a3db5d0a0af9
and daef52bab1fd26e24e8e9578f8fb33ba1d0cb412, shifting SACKed ranges
below snd_una happened to work because tcp_shifted_skb() was always
(incorrectly) passing in to tcp_sacktag_one() an skb whose end_seq
tcp_shift_skb_data() had already guaranteed was beyond snd_una. Hence
tcp_sacktag_one() never short-circuited and always increased
tp->sacked_out in this case.

After those two fixes, my testing has verified that shifting SACKed
ranges below snd_una could cause tp->sacked_out to go negative with
the following sequence of events:

(1) tcp_shift_skb_data() sees an skb whose end_seq is beyond snd_una,
    then shifts a prefix of that skb that is below snd_una

(2) tcp_shifted_skb() increments the packet count of the
    already-SACKed prev sk_buff

(3) tcp_sacktag_one() sees the end of the new SACKed range is below
    snd_una, so it short-circuits and doesn't increase tp->sacked_out

(5) tcp_clean_rtx_queue() sees the SACKed skb has been ACKed,
    decrements tp->sacked_out by this "inflated" pcount that was
    missing a matching increase in tp->sacked_out, and hence
    tp->sacked_out underflows to a u32 like 0xFFFFFFFF, which casted
    to s32 is negative.

(6) this leads to the warnings seen in the recent "WARNING: at
    net/ipv4/tcp_input.c:3418" thread on the netdev list; e.g.:
    tcp_input.c:3418  WARN_ON((int)tp->sacked_out < 0);

More generally, I think this bug can be tickled in some cases where
two or more ACKs from the receiver are lost and then a DSACK arrives
that is immediately above an existing SACKed skb in the write queue.

This fix changes tcp_shift_skb_data() to abort this sequence at step
(1) in the scenario above by noticing that the bytes are below snd_una
and not shifting them.

Signed-off-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: don't fragment SACKed skbs in tcp_mark_head_lost()

2012-03-19T15:57:46+00:00

[ Upstream commit c0638c247f559e1a16ee79e54df14bca2cb679ea ]

In tcp_mark_head_lost() we should not attempt to fragment a SACKed skb
to mark the first portion as lost. This is for two primary reasons:

(1) tcp_shifted_skb() coalesces adjacent regions of SACKed skbs. When
doing this, it preserves the sum of their packet counts in order to
reflect the real-world dynamics on the wire. But given that skbs can
have remainders that do not align to MSS boundaries, this packet count
preservation means that for SACKed skbs there is not necessarily a
direct linear relationship between tcp_skb_pcount(skb) and
skb->len. Thus tcp_mark_head_lost()'s previous attempts to fragment
off and mark as lost a prefix of length (packets - oldcnt)*mss from
SACKed skbs were leading to occasional failures of the WARN_ON(len >
skb->len) in tcp_fragment() (which used to be a BUG_ON(); see the
recent "crash in tcp_fragment" thread on netdev).

(2) there is no real point in fragmenting off part of a SACKed skb and
calling tcp_skb_mark_lost() on it, since tcp_skb_mark_lost() is a NOP
for SACKed skbs.

Signed-off-by: Neal Cardwell 
Acked-by: Ilpo Järvinen 
Acked-by: Yuchung Cheng 
Acked-by: Nandita Dukkipati 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: fix false reordering signal in tcp_shifted_skb

2012-03-19T15:57:45+00:00

[ Upstream commit 4c90d3b30334833450ccbb02f452d4972a3c3c3f ]

When tcp_shifted_skb() shifts bytes from the skb that is currently
pointed to by 'highest_sack' then the increment of
TCP_SKB_CB(skb)->seq implicitly advances tcp_highest_sack_seq(). This
implicit advancement, combined with the recent fix to pass the correct
SACKed range into tcp_sacktag_one(), caused tcp_sacktag_one() to think
that the newly SACKed range was before the tcp_highest_sack_seq(),
leading to a call to tcp_update_reordering() with a degree of
reordering matching the size of the newly SACKed range (typically just
1 packet, which is a NOP, but potentially larger).

This commit fixes this by simply calling tcp_sacktag_one() before the
TCP_SKB_CB(skb)->seq advancement that can advance our notion of the
highest SACKed sequence.

Correspondingly, we can simplify the code a little now that
tcp_shifted_skb() should update the lost_cnt_hint in all cases where
skb == tp->lost_skb_hint.

Signed-off-by: Neal Cardwell 
Acked-by: Yuchung Cheng 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: fix tcp_shifted_skb() adjustment of lost_cnt_hint for FACK

2012-03-01T00:34:17+00:00

[ Upstream commit 0af2a0d0576205dda778d25c6c344fc6508fc81d ]

This commit ensures that lost_cnt_hint is correctly updated in
tcp_shifted_skb() for FACK TCP senders. The lost_cnt_hint adjustment
in tcp_sacktag_one() only applies to non-FACK senders, so FACK senders
need their own adjustment.

This applies the spirit of 1e5289e121372a3494402b1b131b41bfe1cf9b7f -
except now that the sequence range passed into tcp_sacktag_one() is
correct we need only have a special case adjustment for FACK.

Signed-off-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: fix range tcp_shifted_skb() passes to tcp_sacktag_one()

2012-03-01T00:34:16+00:00

[ Upstream commit daef52bab1fd26e24e8e9578f8fb33ba1d0cb412 ]

Fix the newly-SACKed range to be the range of newly-shifted bytes.

Previously - since 832d11c5cd076abc0aa1eaf7be96c81d1a59ce41 -
tcp_shifted_skb() incorrectly called tcp_sacktag_one() with the start
and end sequence numbers of the skb it passes in set to the range just
beyond the range that is newly-SACKed.

This commit also removes a special-case adjustment to lost_cnt_hint in
tcp_shifted_skb() since the pre-existing adjustment of lost_cnt_hint
in tcp_sacktag_one() now properly handles this things now that the
correct start sequence number is passed in.

Signed-off-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: allow tcp_sacktag_one() to tag ranges not aligned with skbs

2012-03-01T00:34:16+00:00

[ Upstream commit cc9a672ee522d4805495b98680f4a3db5d0a0af9 ]

This commit allows callers of tcp_sacktag_one() to pass in sequence
ranges that do not align with skb boundaries, as tcp_shifted_skb()
needs to do in an upcoming fix in this patch series.

In fact, now tcp_sacktag_one() does not need to depend on an input skb
at all, which makes its semantics and dependencies more clear.

Signed-off-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: properly update lost_cnt_hint during shifting

2011-11-11T17:36:28+00:00

[ Upstream commit 1e5289e121372a3494402b1b131b41bfe1cf9b7f ]

lost_skb_hint is used by tcp_mark_head_lost() to mark the first unhandled skb.
lost_cnt_hint is the number of packets or sacked packets before the lost_skb_hint;
When shifting a skb that is before the lost_skb_hint, if tcp_is_fack() is ture,
the skb has already been counted in the lost_cnt_hint; if tcp_is_fack() is false,
tcp_sacktag_one() will increase the lost_cnt_hint. So tcp_shifted_skb() does not
need to adjust the lost_cnt_hint by itself. When shifting a skb that is equal to
lost_skb_hint, the shifted packets will not be counted by tcp_mark_head_lost().
So tcp_shifted_skb() should adjust the lost_cnt_hint even tcp_is_fack(tp) is true.

Signed-off-by: Zheng Yan 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: fix validation of D-SACK

2011-10-03T18:40:54+00:00

[ Upstream commit f779b2d60ab95c17f1e025778ed0df3ec2f05d75 ]

D-SACK is allowed to reside below snd_una. But the corresponding check
in tcp_is_sackblock_valid() is the exact opposite. It looks like a typo.

Signed-off-by: Zheng Yan 
Acked-by: Eric Dumazet 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: Make undo_ssthresh arg to tcp_undo_cwr() a bool.

2011-03-23T02:37:11+00:00

Signed-off-by: David S. Miller

tcp: avoid cwnd moderation in undo

2011-03-23T02:36:08+00:00

In the current undo logic, cwnd is moderated after it was restored
to the value prior entering fast-recovery. It was moderated first
in tcp_try_undo_recovery then again in tcp_complete_cwr.

Since the undo indicates recovery was false, these moderations
are not necessary. If the undo is triggered when most of the
outstanding data have been acknowledged, the (restored) cwnd is
falsely pulled down to a small value.

This patch removes these cwnd moderations if cwnd is undone
  a) during fast-recovery
	b) by receiving DSACKs past fast-recovery

Signed-off-by: Yuchung Cheng 
Signed-off-by: David S. Miller