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, 85 insertions, 0 deletions

diff --git a/Documentation/dev-tools/sparse.rst b/Documentation/dev-tools/sparse.rst
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+.. Copyright 2004 Linus Torvalds
+.. Copyright 2004 Pavel Machek <pavel@ucw.cz>
+.. Copyright 2006 Bob Copeland <me@bobcopeland.com>
+
+Sparse
+======
+
+Sparse is a semantic checker for C programs; it can be used to find a
+number of potential problems with kernel code.  See
+https://lwn.net/Articles/689907/ for an overview of sparse; this document
+contains some kernel-specific sparse information.
+More information on sparse, mainly about its internals, can be found in
+its official pages at https://sparse.docs.kernel.org.
+
+
+Using sparse for typechecking
+-----------------------------
+
+"__bitwise" is a type attribute, so you have to do something like this::
+
+        typedef int __bitwise pm_request_t;
+
+        enum pm_request {
+                PM_SUSPEND = (__force pm_request_t) 1,
+                PM_RESUME = (__force pm_request_t) 2
+        };
+
+which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is
+there because sparse will complain about casting to/from a bitwise type,
+but in this case we really _do_ want to force the conversion). And because
+the enum values are all the same type, now "enum pm_request" will be that
+type too.
+
+And with gcc, all the "__bitwise"/"__force stuff" goes away, and it all
+ends up looking just like integers to gcc.
+
+Quite frankly, you don't need the enum there. The above all really just
+boils down to one special "int __bitwise" type.
+
+So the simpler way is to just do::
+
+        typedef int __bitwise pm_request_t;
+
+        #define PM_SUSPEND ((__force pm_request_t) 1)
+        #define PM_RESUME ((__force pm_request_t) 2)
+
+and you now have all the infrastructure needed for strict typechecking.
+
+One small note: the constant integer "0" is special. You can use a
+constant zero as a bitwise integer type without sparse ever complaining.
+This is because "bitwise" (as the name implies) was designed for making
+sure that bitwise types don't get mixed up (little-endian vs big-endian
+vs cpu-endian vs whatever), and there the constant "0" really _is_
+special.
+
+Getting sparse
+--------------
+
+You can get tarballs of the latest released versions from:
+https://www.kernel.org/pub/software/devel/sparse/dist/
+
+Alternatively, you can get snapshots of the latest development version
+of sparse using git to clone::
+
+        git://git.kernel.org/pub/scm/devel/sparse/sparse.git
+
+Once you have it, just do::
+
+        make
+        make install
+
+as a regular user, and it will install sparse in your ~/bin directory.
+
+Using sparse
+------------
+
+Do a kernel make with "make C=1" to run sparse on all the C files that get
+recompiled, or use "make C=2" to run sparse on the files whether they need to
+be recompiled or not.  The latter is a fast way to check the whole tree if you
+have already built it.
+
+The optional make variable CF can be used to pass arguments to sparse.  The
+build system passes -Wbitwise to sparse automatically.
+
+Note that sparse defines the __CHECKER__ preprocessor symbol.