<p><b>@fjmolinas</b> commented on this pull request.</p>

<hr>

<p>In <a href="https://github.com/RIOT-OS/RIOT/pull/11818#discussion_r328255555">makefiles/suit.v4.inc.mk</a>:</p>
<pre style='color:#555'>> +
+ifeq (1, $(RIOT_CI_BUILD))
+  SUIT_KEY_DIR ?= $(BINDIR)
+else
+  SUIT_KEY_DIR ?= $(RIOTBASE)/keys
+endif
+
+SUIT_SEC ?= $(SUIT_KEY_DIR)/$(SUIT_KEY)
+SUIT_PUB ?= $(SUIT_KEY_DIR)/$(SUIT_KEY).pub
+
+SUIT_PUB_HDR = $(BINDIR)/riotbuild/public_key.h
+SUIT_PUB_HDR_DIR = $(dir $(SUIT_PUB_HDR))
+CFLAGS += -I$(SUIT_PUB_HDR_DIR)
+BUILDDEPS += $(SUIT_PUB_HDR)
+
+$(SUIT_SEC) $(SUIT_PUB): | $(CLEAN)
</pre>
⬇️ Suggested change
<pre style="color: #555">-$(SUIT_SEC) $(SUIT_PUB): | $(CLEAN)
+$(SUIT_SEC) $(SUIT_PUB): $(CLEAN)
</pre>

<p>If I understand <code>order-only prerequesites</code> (and I'm not sure I do), the current situation makes it that <code>$(SUIT_SEC) $(SUIT_PUB)</code> don't need to be recompiled even if <code>$(CLEAN)</code> has changed (in this case is executed). This would be no Issue since normally <code>$(SUIT_SEC) $(SUIT_PUB)</code>  will be recompiled since they would be deleted. But if <code>-j</code> is used make will see <code>$(SUIT_SEC) $(SUIT_PUB)</code> hase not changed and has no <code>normal pre-requisite</code> and since <code>$(CLEAN)</code> is order only it will execute them in parallel and every other compilation will fail.</p>
<p>At least compilation stopped failing for after changing that, I was running this command:</p>
<pre><code>docker run -ti --rm -v $(pwd):/data/riotbuild -u $(id -u) riot/riotbuild:latest make RIOT_CI_BUILD=1 BOARD=samr21-xpro -Cexamples/suit_update clean all -j8
</code></pre>

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