<p>laforge <strong>submitted</strong> this change.</p><p><a href="https://gerrit.osmocom.org/c/osmocom-bb/+/19201">View Change</a></p><div style="white-space:pre-wrap">Approvals:
laforge: Looks good to me, approved
pespin: Looks good to me, but someone else must approve
Jenkins Builder: Verified
</div><pre style="font-family: monospace,monospace; white-space: pre-wrap;">trxcon/scheduler: check TDMA frame order, drop out of order bursts<br><br>When running together with fake_trx.py (mostly used back-end), it<br>is currently possible that Downlink bursts are received in a wrong<br>order if more than one transceiver is configured (multi-trx mode).<br><br>This is how it looks like:<br><br> DTRXD DEBUG trx_if.c:612 RX burst tn=3 fn=629 rssi=-86 toa=0<br> DSCHD DEBUG sched_lchan_tchf.c:60 Traffic received on TCH/F: fn=629 ts=3 bid=1<br> DTRXD DEBUG trx_if.c:612 RX burst tn=3 fn=630 rssi=-86 toa=0<br> DSCHD DEBUG sched_lchan_tchf.c:60 Traffic received on TCH/F: fn=630 ts=3 bid=2<br> DTRXD DEBUG trx_if.c:612 RX burst tn=3 fn=631 rssi=-86 toa=0<br> DSCHD DEBUG sched_lchan_tchf.c:60 Traffic received on TCH/F: fn=631 ts=3 bid=3<br><br> DTRXD DEBUG trx_if.c:612 RX burst tn=3 fn=633 (!) rssi=-86 toa=0<br> DSCHD NOTICE sched_trx.c:663 Substituting (!) lost TDMA frame 632 on TCH/F<br> DSCHD DEBUG sched_lchan_tchf.c:60 Traffic received on TCH/F: fn=632 ts=3 bid=0<br> DSCHD DEBUG sched_lchan_tchf.c:60 Traffic received on TCH/F: fn=633 ts=3 bid=1<br><br> DTRXD DEBUG trx_if.c:612 RX burst tn=3 fn=632 (!) rssi=-86 toa=0<br> DTRXD NOTICE sched_trx.c:640 Too many (>104) contiguous TDMA frames elapsed (2715647)<br> since the last processed fn=633 (current fn=632)<br><br>so here a burst with TDMA fn=633 was received earlier than a burst<br>with TDMA fn=632. The burst loss detection logic considered the<br>latter one as lost, and substituted it with a dummy burst. When<br>finally the out-of-order burst with TDMA fn=632 was received, we<br>got the large number of allegedly elapsed frames:<br><br> ((632 + 2715648) - 633) % 2715648 == 2715647<br><br>Given that late bursts get substituted, the best thing we can do<br>is to reject them and log an error. Passing them to the logical<br>channel handler (again) might lead to undefined behaviour.<br><br>Change-Id: I873c8555ea2ca190b1689227bb0fdcba87188772<br>Related: OS#4658, OS#4546<br>---<br>M src/host/trxcon/sched_trx.c<br>1 file changed, 26 insertions(+), 5 deletions(-)<br><br></pre><pre style="font-family: monospace,monospace; white-space: pre-wrap;"><span>diff --git a/src/host/trxcon/sched_trx.c b/src/host/trxcon/sched_trx.c</span><br><span>index 9195b33..0025e0c 100644</span><br><span>--- a/src/host/trxcon/sched_trx.c</span><br><span>+++ b/src/host/trxcon/sched_trx.c</span><br><span>@@ -625,7 +625,7 @@</span><br><span> {</span><br><span> const struct trx_multiframe *mf;</span><br><span> const struct trx_frame *fp;</span><br><span style="color: hsl(0, 100%, 40%);">- unsigned int elapsed, i;</span><br><span style="color: hsl(120, 100%, 40%);">+ int elapsed, i;</span><br><span> </span><br><span> /* Wait until at least one TDMA frame is processed */</span><br><span> if (lchan->tdma.num_proc == 0)</span><br><span>@@ -634,10 +634,28 @@</span><br><span> /* Short alias for the current multiframe */</span><br><span> mf = lchan->ts->mf_layout;</span><br><span> </span><br><span style="color: hsl(0, 100%, 40%);">- /* How many frames elapsed since the last one? */</span><br><span style="color: hsl(0, 100%, 40%);">- elapsed = GSM_TDMA_FN_SUB(fn, lchan->tdma.last_proc);</span><br><span style="color: hsl(120, 100%, 40%);">+ /* Calculate how many frames elapsed since the last received one.</span><br><span style="color: hsl(120, 100%, 40%);">+ * The algorithm is based on GSM::FNDelta() from osmo-trx. */</span><br><span style="color: hsl(120, 100%, 40%);">+ elapsed = fn - lchan->tdma.last_proc;</span><br><span style="color: hsl(120, 100%, 40%);">+ if (elapsed >= GSM_TDMA_HYPERFRAME / 2)</span><br><span style="color: hsl(120, 100%, 40%);">+ elapsed -= GSM_TDMA_HYPERFRAME;</span><br><span style="color: hsl(120, 100%, 40%);">+ else if (elapsed < -GSM_TDMA_HYPERFRAME / 2)</span><br><span style="color: hsl(120, 100%, 40%);">+ elapsed += GSM_TDMA_HYPERFRAME;</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ /* Check TDMA frame order (wrong order is possible with fake_trx.py, see OS#4658) */</span><br><span style="color: hsl(120, 100%, 40%);">+ if (elapsed < 0) {</span><br><span style="color: hsl(120, 100%, 40%);">+ /* This burst has already been substituted by a dummy burst (all bits set to zero),</span><br><span style="color: hsl(120, 100%, 40%);">+ * so better drop it. Otherwise we risk to get undefined behavior in handler(). */</span><br><span style="color: hsl(120, 100%, 40%);">+ LOGP(DSCHD, LOGL_ERROR, "(%s) Rx burst with fn=%u older than the last "</span><br><span style="color: hsl(120, 100%, 40%);">+ "processed fn=%u (see OS#4658) => dropping\n",</span><br><span style="color: hsl(120, 100%, 40%);">+ trx_lchan_desc[lchan->type].name,</span><br><span style="color: hsl(120, 100%, 40%);">+ fn, lchan->tdma.last_proc);</span><br><span style="color: hsl(120, 100%, 40%);">+ return -EALREADY;</span><br><span style="color: hsl(120, 100%, 40%);">+ }</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ /* Check how many frames we (potentially) need to compensate */</span><br><span> if (elapsed > mf->period) {</span><br><span style="color: hsl(0, 100%, 40%);">- LOGP(DSCHD, LOGL_NOTICE, "Too many (>%u) contiguous TDMA frames elapsed (%u) "</span><br><span style="color: hsl(120, 100%, 40%);">+ LOGP(DSCHD, LOGL_NOTICE, "Too many (>%u) contiguous TDMA frames elapsed (%d) "</span><br><span> "since the last processed fn=%u (current %u)\n",</span><br><span> mf->period, elapsed, lchan->tdma.last_proc, fn);</span><br><span> return -EIO;</span><br><span>@@ -687,6 +705,7 @@</span><br><span> trx_lchan_rx_func *handler;</span><br><span> enum trx_lchan_type chan;</span><br><span> uint8_t offset, bid;</span><br><span style="color: hsl(120, 100%, 40%);">+ int rc;</span><br><span> </span><br><span> /* Check whether required timeslot is allocated and configured */</span><br><span> ts = trx->ts_list[tn];</span><br><span>@@ -720,7 +739,9 @@</span><br><span> return 0;</span><br><span> </span><br><span> /* Compensate lost TDMA frames (if any) */</span><br><span style="color: hsl(0, 100%, 40%);">- subst_frame_loss(lchan, handler, fn);</span><br><span style="color: hsl(120, 100%, 40%);">+ rc = subst_frame_loss(lchan, handler, fn);</span><br><span style="color: hsl(120, 100%, 40%);">+ if (rc == -EALREADY)</span><br><span style="color: hsl(120, 100%, 40%);">+ return rc;</span><br><span> </span><br><span> /* Perform A5/X decryption if required */</span><br><span> if (lchan->a5.algo)</span><br><span></span><br></pre><p>To view, visit <a href="https://gerrit.osmocom.org/c/osmocom-bb/+/19201">change 19201</a>. 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<div style="display:none"> Gerrit-Project: osmocom-bb </div>
<div style="display:none"> Gerrit-Branch: master </div>
<div style="display:none"> Gerrit-Change-Id: I873c8555ea2ca190b1689227bb0fdcba87188772 </div>
<div style="display:none"> Gerrit-Change-Number: 19201 </div>
<div style="display:none"> Gerrit-PatchSet: 5 </div>
<div style="display:none"> Gerrit-Owner: fixeria <vyanitskiy@sysmocom.de> </div>
<div style="display:none"> Gerrit-Reviewer: Jenkins Builder </div>
<div style="display:none"> Gerrit-Reviewer: fixeria <vyanitskiy@sysmocom.de> </div>
<div style="display:none"> Gerrit-Reviewer: laforge <laforge@osmocom.org> </div>
<div style="display:none"> Gerrit-Reviewer: neels <nhofmeyr@sysmocom.de> </div>
<div style="display:none"> Gerrit-Reviewer: pespin <pespin@sysmocom.de> </div>
<div style="display:none"> Gerrit-MessageType: merged </div>