netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 74 insertions, 0 deletions

diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
new file mode 100644
index 000000000..01a37ec87
--- /dev/null
+++ b/scripts/Makefile.modfinal
@@ -0,0 +1,74 @@
+# SPDX-License-Identifier: GPL-2.0-only
+# ===========================================================================
+# Module final link
+# ===========================================================================
+
+PHONY := __modfinal
+__modfinal:
+
+include $(objtree)/include/config/auto.conf
+include $(srctree)/scripts/Kbuild.include
+include $(srctree)/scripts/Makefile.lib
+
+# find all modules listed in modules.order
+modules := $(call read-file, modules.order)
+
+__modfinal: $(modules:%.o=%.ko)
+	@:
+
+# modname and part-of-module are set to make c_flags define proper module flags
+modname = $(notdir $(@:.mod.o=))
+part-of-module = y
+GCOV_PROFILE := n
+ccflags-remove-y := $(CC_FLAGS_CFI)
+
+%.mod.o: %.mod.c FORCE
+	$(call if_changed_rule,cc_o_c)
+
+.module-common.o: $(srctree)/scripts/module-common.c FORCE
+	$(call if_changed_rule,cc_o_c)
+
+ifneq ($(WARN_ON_UNUSED_TRACEPOINTS),)
+cmd_check_tracepoint = $(objtree)/scripts/tracepoint-update --module $<;
+endif
+
+quiet_cmd_ld_ko_o = LD [M]  $@
+      cmd_ld_ko_o =							\
+	$(LD) -r $(KBUILD_LDFLAGS)					\
+		$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE)		\
+		-T $(objtree)/scripts/module.lds -o $@ $(filter %.o, $^)
+
+quiet_cmd_btf_ko = BTF [M] $@
+      cmd_btf_ko = 							\
+	if [ ! -f $(objtree)/vmlinux ]; then				\
+		printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \
+	else	\
+		$(CONFIG_SHELL) $(srctree)/scripts/gen-btf.sh --btf_base $(objtree)/vmlinux $@; \
+	fi;
+
+# Re-generate module BTFs if either module's .ko or vmlinux changed
+%.ko: %.o %.mod.o .module-common.o $(objtree)/scripts/module.lds $(and $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),$(objtree)/vmlinux) FORCE
+	+$(call if_changed,ld_ko_o)
+ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	+$(if $(newer-prereqs),$(call cmd,btf_ko))
+endif
+	+$(call cmd,check_tracepoint)
+
+targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o) .module-common.o
+
+# Add FORCE to the prerequisites of a target to force it to be always rebuilt.
+# ---------------------------------------------------------------------------
+
+PHONY += FORCE
+FORCE:
+
+# Read all saved command lines and dependencies for the $(targets) we
+# may be building above, using $(if_changed{,_dep}). As an
+# optimization, we don't need to read them if the target does not
+# exist, we will rebuild anyway in that case.
+
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+.PHONY: $(PHONY)