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Commit 41a2901e authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Remove SPARSE_RCU_POINTER Kconfig option 



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: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
parent c4a09ff7

Documentation/RCU/Design/Requirements/Requirements.html

+3 −6
Original line number Diff line number Diff line
@@ -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>.

Documentation/RCU/checklist.txt

+4 −4
Original line number Diff line number Diff line
@@ -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

Documentation/dev-tools/sparse.rst

+0 −6
Original line number Diff line number Diff line
@@ -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.

include/linux/compiler.h

+0 −4
Original line number Diff line number Diff line
@@ -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 *);

lib/Kconfig.debug

+0 −15
Original line number Diff line number Diff line
@@ -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