doc-rst: Break shell command sequences on failure

As $(SHELL) doesn't include the -e option, any loop or other sequence
needs to include explicit checks for failing commands.

Fixes: 609afe6b ("Documentation/sphinx: build the media intermediate ...")
Fixes: 606b9ac8 ("doc-rst: generic way to build only sphinx sub-folders")
Fixes: cd21379b ("doc-rst: generic way to build PDF of sub-folders")
Tested-by: Markus Heiser <markus.heiser@darmarit.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/Makefile.sphinx

@@ -43,7 +43,7 @@ ALLSPHINXOPTS   =  $(KERNELDOC_CONF) $(PAPEROPT_$(PAPER)) $(SPHINXOPTS)
 I18NSPHINXOPTS  = $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
 
 # commands; the 'cmd' from scripts/Kbuild.include is not *loopable*
-loop_cmd = $(echo-cmd) $(cmd_$(1))
+loop_cmd = $(echo-cmd) $(cmd_$(1)) || exit;
 
 # $2 sphinx builder e.g. "html"
 # $3 name of the build subfolder / e.g. "media", used as:
@@ -54,7 +54,7 @@ loop_cmd = $(echo-cmd) $(cmd_$(1))
 #    e.g. "media" for the linux-tv book-set at ./Documentation/media
 
 quiet_cmd_sphinx = SPHINX  $@ --> file://$(abspath $(BUILDDIR)/$3/$4)
-      cmd_sphinx = $(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) $(build)=Documentation/media $2;\
+      cmd_sphinx = $(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) $(build)=Documentation/media $2 && \
 	BUILDDIR=$(abspath $(BUILDDIR)) SPHINX_CONF=$(abspath $(srctree)/$(src)/$5/$(SPHINX_CONF)) \
 	$(SPHINXBUILD) \
 	-b $2 \
@@ -63,7 +63,7 @@ quiet_cmd_sphinx = SPHINX  $@ --> file://$(abspath $(BUILDDIR)/$3/$4)
 	-D version=$(KERNELVERSION) -D release=$(KERNELRELEASE) \
 	$(ALLSPHINXOPTS) \
 	$(abspath $(srctree)/$(src)/$5) \
-	$(abspath $(BUILDDIR)/$3/$4);
+	$(abspath $(BUILDDIR)/$3/$4)
 
 htmldocs:
 	@$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,html,$(var),,$(var)))
@@ -80,7 +80,7 @@ pdfdocs:
 else # HAVE_PDFLATEX
 
 pdfdocs: latexdocs
-	$(foreach var,$(SPHINXDIRS), $(MAKE) PDFLATEX=$(PDFLATEX) LATEXOPTS="$(LATEXOPTS)" -C $(BUILDDIR)/$(var)/latex;)
+	$(foreach var,$(SPHINXDIRS), $(MAKE) PDFLATEX=$(PDFLATEX) LATEXOPTS="$(LATEXOPTS)" -C $(BUILDDIR)/$(var)/latex || exit;)
 
 endif # HAVE_PDFLATEX