On Mon, May 18, 2015 at 07:48:02PM +0200, Nicholas Mc Guire wrote:
> static code checking with coccinelle was unhappy with:
> ./kernel/locking/percpu-rwsem.c:113 WARNING: return of wrong type
> int != unsigned int
>
>
> current state:
>
> include/linux/percpu-rwsem.h:
> struct percpu_rw_semaphore {
> unsigned int __percpu *fast_read_ctr;
> ...
> atomic_t slow_read_ctr;
>
> allocated as int:
>
> int __percpu_init_rwsem(struct percpu_rw_semaphore *brw,
> const char *name, struct lock_class_key *rwsem_key)
> {
> brw->fast_read_ctr = alloc_percpu(int);
>
> used compliant with type int in:
>
> static bool update_fast_ctr(struct percpu_rw_semaphore *brw,
> unsigned int val)
> usage (2):
> update_fast_ctr(brw, +1)
> update_fast_ctr(brw, -1)
>
> so val should be int here not unsigned int
>
> static int clear_fast_ctr(struct percpu_rw_semaphore *brw)
> usage (1):
> atomic_add(clear_fast_ctr(brw), &brw->slow_read_ctr);
>
> slow_read_ctr is atomic_t which is int so it would be consistent here to
> have fast_read_ctr being changed to int as well.
>
> This patch changes:
> fast_read_ctr to int
> clear_fast_ctr():sum to int
> update_fast_ctr():val to int
> to make usage of fast_read_ctr consistent with respect to type.
>
> ( Patch was build tested with x86_64_defconfig +
> CONFIG_UPROBE_EVENT (implies CONFIG_PERCPU_RWSEM=y))
>
> Signed-off-by: Nicholas Mc Guire <hof...@osadl.org>
So the value is unsigned by purpose; that said we should never cross the
2G I think, so it really doesn't matter much.
Cc'ed Oleg who wrote this code, left the rest of the msg for his
convencience.
That said; Oleg, should I post those patches implementing percpu-rwsem
with the stuff we did for the hotplug lock a while back? I think I
actually have those around somewhere.
> ---
> include/linux/percpu-rwsem.h | 2 +-
> kernel/locking/percpu-rwsem.c | 4 ++--
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
> index 3e88c9a..ba37dbe 100644
> --- a/include/linux/percpu-rwsem.h
> +++ b/include/linux/percpu-rwsem.h
> @@ -8,7 +8,7 @@
> #include <linux/lockdep.h>
>
> struct percpu_rw_semaphore {
> - unsigned int __percpu *fast_read_ctr;
> + int __percpu *fast_read_ctr;
> atomic_t write_ctr;
> struct rw_semaphore rw_sem;
> atomic_t slow_read_ctr;
> diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
> index 652a8ee..002837d 100644
> --- a/kernel/locking/percpu-rwsem.c
> +++ b/kernel/locking/percpu-rwsem.c
> @@ -52,7 +52,7 @@ void percpu_free_rwsem(struct percpu_rw_semaphore *brw)
> * reader inside the critical section. See the comments in down_write and
> * up_write below.
> */
> -static bool update_fast_ctr(struct percpu_rw_semaphore *brw, unsigned int
> val)
> +static bool update_fast_ctr(struct percpu_rw_semaphore *brw, int val)
> {
> bool success = false;
>
> @@ -102,7 +102,7 @@ void percpu_up_read(struct percpu_rw_semaphore *brw)
>
> static int clear_fast_ctr(struct percpu_rw_semaphore *brw)
> {
> - unsigned int sum = 0;
> + int sum = 0;
> int cpu;
>
> for_each_possible_cpu(cpu) {
> --
> 1.7.10.4
>
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