[PATCH tip/core/rcu 80/88] rcu: Remove SPARSE_RCU_POINTER Kconfig option

From: Paul E. McKenney
Date: Thu May 25 2017 - 18:09:45 EST

The sparse-based checking for non-RCU accesses to RCU-protected pointers
has been around for a very long time, and it is now the only type of
sparse-based checking that is optional. This commit therefore makes
it unconditional.

Reported-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
---
Documentation/RCU/Design/Requirements/Requirements.html | 9 +++------
Documentation/RCU/checklist.txt | 8 ++++----
Documentation/dev-tools/sparse.rst | 6 ------
include/linux/compiler.h | 4 ----
lib/Kconfig.debug | 15 ---------------
lib/Makefile | 3 ---
.../testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt | 4 ----
7 files changed, 7 insertions(+), 42 deletions(-)

diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html
index 8c94fc1d1c84..0e6550a8c926 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.html
+++ b/Documentation/RCU/Design/Requirements/Requirements.html
@@ -559,9 +559,7 @@ The <tt>rcu_access_pointer()</tt> on line&nbsp;6 is similar to
For <tt>remove_gp_synchronous()</tt>, as long as all modifications
to <tt>gp</tt> are carried out while holding <tt>gp_lock</tt>,
the above optimizations are harmless.
- However,
- with <tt>CONFIG_SPARSE_RCU_POINTER=y</tt>,
- <tt>sparse</tt> will complain if you
+ However, <tt>sparse</tt> will complain if you
define <tt>gp</tt> with <tt>__rcu</tt> and then
access it without using
either <tt>rcu_access_pointer()</tt> or <tt>rcu_dereference()</tt>.
@@ -1978,9 +1976,8 @@ guard against mishaps and misuse:
and <tt>rcu_dereference()</tt>, perhaps (incorrectly)
substituting a simple assignment.
To catch this sort of error, a given RCU-protected pointer may be
- tagged with <tt>__rcu</tt>, after which running sparse
- with <tt>CONFIG_SPARSE_RCU_POINTER=y</tt> will complain
- about simple-assignment accesses to that pointer.
+ tagged with <tt>__rcu</tt>, after which sparse
+ will complain about simple-assignment accesses to that pointer.
Arnd Bergmann made me aware of this requirement, and also
supplied the needed
<a href="https://lwn.net/Articles/376011/";>patch series</a>.
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index 877947130ebe..6beda556faf3 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -413,11 +413,11 @@ over a rather long period of time, but improvements are always welcome!
read-side critical sections. It is the responsibility of the
RCU update-side primitives to deal with this.

-17. Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and the
- __rcu sparse checks (enabled by CONFIG_SPARSE_RCU_POINTER) to
- validate your RCU code. These can help find problems as follows:
+17. Use CONFIG_PROVE_LOCKING, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and the
+ __rcu sparse checks to validate your RCU code. These can help
+ find problems as follows:

- CONFIG_PROVE_RCU: check that accesses to RCU-protected data
+ CONFIG_PROVE_LOCKING: check that accesses to RCU-protected data
structures are carried out under the proper RCU
read-side critical section, while holding the right
combination of locks, or whatever other conditions
diff --git a/Documentation/dev-tools/sparse.rst b/Documentation/dev-tools/sparse.rst
index ffdcc97f6f5a..78aa00a604a0 100644
--- a/Documentation/dev-tools/sparse.rst
+++ b/Documentation/dev-tools/sparse.rst
@@ -103,9 +103,3 @@ 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.
-
-Checking RCU annotations
-~~~~~~~~~~~~~~~~~~~~~~~~
-
-RCU annotations are not checked by default. To enable RCU annotation
-checks, include -DCONFIG_SPARSE_RCU_POINTER in your CF flags.
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index f8110051188f..707242fdbb89 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -17,11 +17,7 @@
# define __release(x) __context__(x,-1)
# define __cond_lock(x,c) ((c) ? ({ __acquire(x); 1; }) : 0)
# define __percpu __attribute__((noderef, address_space(3)))
-#ifdef CONFIG_SPARSE_RCU_POINTER
# define __rcu __attribute__((noderef, address_space(4)))
-#else /* CONFIG_SPARSE_RCU_POINTER */
-# define __rcu
-#endif /* CONFIG_SPARSE_RCU_POINTER */
# define __private __attribute__((noderef))
extern void __chk_user_ptr(const volatile void __user *);
extern void __chk_io_ptr(const volatile void __iomem *);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 762deab304fe..498d5dd63bf4 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1306,21 +1306,6 @@ menu "RCU Debugging"
config PROVE_RCU
def_bool PROVE_LOCKING

-config SPARSE_RCU_POINTER
- bool "RCU debugging: sparse-based checks for pointer usage"
- default n
- help
- This feature enables the __rcu sparse annotation for
- RCU-protected pointers. This annotation will cause sparse
- to flag any non-RCU used of annotated pointers. This can be
- helpful when debugging RCU usage. Please note that this feature
- is not intended to enforce code cleanliness; it is instead merely
- a debugging aid.
-
- Say Y to make sparse flag questionable use of RCU-protected pointers
-
- Say N if you are unsure.
-
config TORTURE_TEST
tristate
default n
diff --git a/lib/Makefile b/lib/Makefile
index 0166fbc0fa81..07fbe6a75692 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -25,9 +25,6 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
earlycpio.o seq_buf.o siphash.o \
nmi_backtrace.o nodemask.o win_minmax.o

-CFLAGS_radix-tree.o += -DCONFIG_SPARSE_RCU_POINTER
-CFLAGS_idr.o += -DCONFIG_SPARSE_RCU_POINTER
-
lib-$(CONFIG_MMU) += ioremap.o
lib-$(CONFIG_SMP) += cpumask.o
lib-$(CONFIG_DMA_NOOP_OPS) += dma-noop.o
diff --git a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
index b778a28f1386..c5c29fb7438c 100644
--- a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
+++ b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
@@ -74,10 +74,6 @@ CONFIG_TINY_RCU

These are controlled by CONFIG_PREEMPT and/or CONFIG_SMP.

-CONFIG_SPARSE_RCU_POINTER
-
- Makes sense only for sparse runs, not for kernel builds.
-
CONFIG_SRCU
CONFIG_TASKS_RCU

--
2.5.2