selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 137 insertions, 0 deletions

diff --git a/tools/build/Build.include b/tools/build/Build.include
new file mode 100644
index 000000000..cd0baa7a1
--- /dev/null
+++ b/tools/build/Build.include
@@ -0,0 +1,137 @@
+###
+# build: Generic definitions
+#
+#  Lots of this code have been borrowed or heavily inspired from parts
+#  of kbuild code, which is not credited, but mostly developed by:
+#
+#  Copyright (C) Sam Ravnborg <sam@mars.ravnborg.org>, 2015
+#  Copyright (C) Linus Torvalds <torvalds@linux-foundation.org>, 2015
+#
+
+###
+# Convenient variables
+comma   := ,
+squote  := '
+pound   := \#
+empty   :=
+space   := $(empty) $(empty)
+
+###
+# Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
+dot-target = $(dir $@).$(notdir $@)
+
+###
+# filename of target with directory and extension stripped
+basetarget = $(basename $(notdir $@))
+
+###
+# The temporary file to save gcc -MD generated dependencies must not
+# contain a comma
+depfile = $(subst $(comma),_,$(dot-target).d)
+
+###
+# Check if both arguments has same arguments. Result is empty string if equal.
+arg-check = $(strip $(filter-out $(cmd_$(1)), $(cmd_$@)) \
+                    $(filter-out $(cmd_$@),   $(cmd_$(1))) )
+
+###
+# Escape single quote for use in echo statements
+escsq = $(subst $(squote),'\$(squote)',$1)
+
+# Echo command
+# Short version is used, if $(quiet) equals `quiet_', otherwise full one.
+echo-cmd = $(if $($(quiet)cmd_$(1)),\
+           echo '  $(call escsq,$($(quiet)cmd_$(1)))';)
+
+###
+# Replace >$< with >$$< to preserve $ when reloading the .cmd file
+# (needed for make)
+# Replace >#< with >$(pound)< to avoid starting a comment in the .cmd file
+# (needed for make)
+# Replace >'< with >'\''< to be able to enclose the whole string in '...'
+# (needed for the shell)
+make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1)))))
+
+###
+# Find any prerequisites that is newer than target or that does not exist.
+# PHONY targets skipped in both cases.
+any-prereq = $(filter-out $(PHONY),$?) $(filter-out $(PHONY) $(wildcard $^),$^)
+
+###
+# Copy dependency data into .cmd file
+#  - gcc -M dependency info
+#  - command line to create object 'cmd_object :='
+dep-cmd = $(if $(wildcard $(fixdep)),                                           \
+           $(fixdep) $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;           \
+           rm -f $(depfile);                                                    \
+           mv -f $(dot-target).tmp $(dot-target).cmd,                           \
+           printf '$(pound) cannot find fixdep (%s)\n' $(fixdep) > $(dot-target).cmd; \
+           printf '$(pound) using basic dep data\n\n' >> $(dot-target).cmd;           \
+           cat $(depfile) >> $(dot-target).cmd;                                 \
+           printf '\n%s\n' 'cmd_$@ := $(make-cmd)' >> $(dot-target).cmd)
+
+###
+# if_changed_dep  - execute command if any prerequisite is newer than
+#                   target, or command line has changed and update
+#                   dependencies in the cmd file
+if_changed_dep = $(if $(strip $(any-prereq) $(arg-check)),         \
+                  @set -e;                                         \
+                  $(echo-cmd) $(cmd_$(1));                         \
+                  $(dep-cmd))
+
+# if_changed      - execute command if any prerequisite is newer than
+#                   target, or command line has changed
+if_changed = $(if $(strip $(any-prereq) $(arg-check)),                   \
+              @set -e;                                                   \
+              $(echo-cmd) $(cmd_$(1));                                   \
+              printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd)
+
+###
+# C flags to be used in rule definitions, includes:
+# - depfile generation
+# - global $(CFLAGS)
+# - per target C flags
+# - per object C flags
+# - BUILD_STR macro to allow '-D"$(variable)"' constructs
+c_flags_1 = -Wp,-MD,$(depfile) -Wp,-MT,$@ $(CFLAGS) -D"BUILD_STR(s)=\#s" $(CFLAGS_$(basetarget).o) $(CFLAGS_$(obj))
+c_flags_2 = $(filter-out $(CFLAGS_REMOVE_$(basetarget).o), $(c_flags_1))
+c_flags   = $(filter-out $(CFLAGS_REMOVE_$(obj)), $(c_flags_2))
+cxx_flags = -Wp,-MD,$(depfile) -Wp,-MT,$@ $(CXXFLAGS) -D"BUILD_STR(s)=\#s" $(CXXFLAGS_$(basetarget).o) $(CXXFLAGS_$(obj))
+
+###
+# Rust flags to be used on rule definition, includes:
+# - global $(RUST_FLAGS)
+# - per target Rust flags
+# - per object Rust flags
+rust_flags_1 = $(RUST_FLAGS) $(RUST_FLAGS_$(basetarget).o) $(RUST_FLAGS_$(obj))
+rust_flags_2 = $(filter-out $(RUST_FLAGS_REMOVE_$(basetarget).o), $(rust_flags_1))
+rust_flags   = $(filter-out $(RUST_FLAGS_REMOVE_$(obj)), $(rust_flags_2))
+
+###
+## HOSTCC C flags
+
+host_c_flags = -Wp,-MD,$(depfile) -Wp,-MT,$@ $(HOSTCFLAGS) -D"BUILD_STR(s)=\#s" $(HOSTCFLAGS_$(basetarget).o) $(HOSTCFLAGS_$(obj))
+
+# output directory for tests below
+TMPOUT = .tmp_$$$$
+
+# try-run
+# Usage: option = $(call try-run, $(CC)...-o "$$TMP",option-ok,otherwise)
+# Exit code chooses option. "$$TMP" serves as a temporary file and is
+# automatically cleaned up.
+try-run = $(shell set -e;		\
+	TMP=$(TMPOUT)/tmp;		\
+	mkdir -p $(TMPOUT);		\
+	trap "rm -rf $(TMPOUT)" EXIT;	\
+	if ($(1)) >/dev/null 2>&1;	\
+	then echo "$(2)";		\
+	else echo "$(3)";		\
+	fi)
+
+# cc-option
+# Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)
+cc-option = $(call try-run, \
+	$(CC) -Werror $(1) -c -x c /dev/null -o "$$TMP",$(1),$(2))
+
+# delete partially updated (i.e. corrupted) files on error
+.DELETE_ON_ERROR: