Re: [PATCH RESEND -rcu/kcsan] kcsan: Prefer __always_inline for fast-path

[Paul E. McKenney]

On Fri, Dec 13, 2019 at 09:49:46PM +0100, Marco Elver wrote:
> Prefer __always_inline for fast-path functions that are called outside
> of user_access_save, to avoid generating UACCESS warnings when
> optimizing for size (CC_OPTIMIZE_FOR_SIZE). It will also avoid future
> surprises with compiler versions that change the inlining heuristic even
> when optimizing for performance.
> 
> Report: http://lkml.kernel.org/r/58708908-84a0-0a81-a836-ad97e33dbb62@xxxxxxxxxxxxx
> Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> # build-tested
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>

Queued for review and testing, thank you!

							Thanx, Paul

> ---
> Version rebased on -rcu/kcsan.
> 
> There are 3 locations that would conflict with the style cleanup in
> -tip/locking/kcsan:
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=locking/kcsan&id=5cbaefe9743bf14c9d3106db0cc19f8cb0a3ca22
> 
> For the conflicting locations the better style is carried over, so that
> upon eventual merge the resolution should be trivial.
> ---
>  kernel/kcsan/atomic.h   |  2 +-
>  kernel/kcsan/core.c     | 17 ++++++++---------
>  kernel/kcsan/encoding.h | 11 +++++------
>  3 files changed, 14 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/kcsan/atomic.h b/kernel/kcsan/atomic.h
> index c9c3fe628011..466e6777533e 100644
> --- a/kernel/kcsan/atomic.h
> +++ b/kernel/kcsan/atomic.h
> @@ -18,7 +18,7 @@
>   * than cast to volatile. Eventually, we hope to be able to remove this
>   * function.
>   */
> -static inline bool kcsan_is_atomic(const volatile void *ptr)
> +static __always_inline bool kcsan_is_atomic(const volatile void *ptr)
>  {
>  	/* only jiffies for now */
>  	return ptr == &jiffies;
> diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> index d9410d58c93e..69870645b631 100644
> --- a/kernel/kcsan/core.c
> +++ b/kernel/kcsan/core.c
> @@ -78,9 +78,8 @@ static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS - 1];
>   */
>  static DEFINE_PER_CPU(long, kcsan_skip);
>  
> -static inline atomic_long_t *find_watchpoint(unsigned long addr, size_t size,
> -					     bool expect_write,
> -					     long *encoded_watchpoint)
> +static __always_inline atomic_long_t *
> +find_watchpoint(unsigned long addr, size_t size, bool expect_write, long *encoded_watchpoint)
>  {
>  	const int slot = watchpoint_slot(addr);
>  	const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK;
> @@ -150,8 +149,8 @@ static inline atomic_long_t *insert_watchpoint(unsigned long addr, size_t size,
>   *	2. the thread that set up the watchpoint already removed it;
>   *	3. the watchpoint was removed and then re-used.
>   */
> -static inline bool try_consume_watchpoint(atomic_long_t *watchpoint,
> -					  long encoded_watchpoint)
> +static __always_inline bool
> +try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint)
>  {
>  	return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint,
>  					       CONSUMED_WATCHPOINT);
> @@ -166,7 +165,7 @@ static inline bool remove_watchpoint(atomic_long_t *watchpoint)
>  	       CONSUMED_WATCHPOINT;
>  }
>  
> -static inline struct kcsan_ctx *get_ctx(void)
> +static __always_inline struct kcsan_ctx *get_ctx(void)
>  {
>  	/*
>  	 * In interrupt, use raw_cpu_ptr to avoid unnecessary checks, that would
> @@ -175,7 +174,7 @@ static inline struct kcsan_ctx *get_ctx(void)
>  	return in_task() ? &current->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
>  }
>  
> -static inline bool is_atomic(const volatile void *ptr)
> +static __always_inline bool is_atomic(const volatile void *ptr)
>  {
>  	struct kcsan_ctx *ctx = get_ctx();
>  
> @@ -199,7 +198,7 @@ static inline bool is_atomic(const volatile void *ptr)
>  	return kcsan_is_atomic(ptr);
>  }
>  
> -static inline bool should_watch(const volatile void *ptr, int type)
> +static __always_inline bool should_watch(const volatile void *ptr, int type)
>  {
>  	/*
>  	 * Never set up watchpoints when memory operations are atomic.
> @@ -232,7 +231,7 @@ static inline void reset_kcsan_skip(void)
>  	this_cpu_write(kcsan_skip, skip_count);
>  }
>  
> -static inline bool kcsan_is_enabled(void)
> +static __always_inline bool kcsan_is_enabled(void)
>  {
>  	return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0;
>  }
> diff --git a/kernel/kcsan/encoding.h b/kernel/kcsan/encoding.h
> index e17bdac0e54b..e527e83ce825 100644
> --- a/kernel/kcsan/encoding.h
> +++ b/kernel/kcsan/encoding.h
> @@ -58,9 +58,8 @@ static inline long encode_watchpoint(unsigned long addr, size_t size,
>  		      (addr & WATCHPOINT_ADDR_MASK));
>  }
>  
> -static inline bool decode_watchpoint(long watchpoint,
> -				     unsigned long *addr_masked, size_t *size,
> -				     bool *is_write)
> +static __always_inline bool
> +decode_watchpoint(long watchpoint, unsigned long *addr_masked, size_t *size, bool *is_write)
>  {
>  	if (watchpoint == INVALID_WATCHPOINT ||
>  	    watchpoint == CONSUMED_WATCHPOINT)
> @@ -77,13 +76,13 @@ static inline bool decode_watchpoint(long watchpoint,
>  /*
>   * Return watchpoint slot for an address.
>   */
> -static inline int watchpoint_slot(unsigned long addr)
> +static __always_inline int watchpoint_slot(unsigned long addr)
>  {
>  	return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS;
>  }
>  
> -static inline bool matching_access(unsigned long addr1, size_t size1,
> -				   unsigned long addr2, size_t size2)
> +static __always_inline bool matching_access(unsigned long addr1, size_t size1,
> +					    unsigned long addr2, size_t size2)
>  {
>  	unsigned long end_range1 = addr1 + size1 - 1;
>  	unsigned long end_range2 = addr2 + size2 - 1;
> -- 
> 2.24.1.735.g03f4e72817-goog
>