[PATCH] printk: remove unneeded dead-store assignment

[PATCH] printk: remove unneeded dead-store assignment

[Lukas Bulwahn]

make clang-analyzer on x86_64 defconfig caught my attention with:

  kernel/printk/printk_ringbuffer.c:885:3: warning:
  Value stored to 'desc' is never read [clang-analyzer-deadcode.DeadStores]
                desc = to_desc(desc_ring, head_id);
                ^

Commit b6cf8b3f3312 ("printk: add lockless ringbuffer") introduced
desc_reserve() with this unneeded dead-store assignment.

As discussed with John Ogness privately, this is probably just some minor
left-over from previous iterations of the ringbuffer implementation. So,
simply remove this unneeded dead assignment to make clang-analyzer happy.

As compilers will detect this unneeded assignment and optimize this anyway,
the resulting object code is identical before and after this change.

No functional change. No change to object code.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
---
applies cleanly on current master and next-20201105

John, please ack.
Petr, please pick this minor non-urgent clean-up patch.

 kernel/printk/printk_ringbuffer.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index 6b1525685277..74e25a1704f2 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -882,8 +882,6 @@ static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out)
 	head_id = atomic_long_read(&desc_ring->head_id); /* LMM(desc_reserve:A) */
 
 	do {
-		desc = to_desc(desc_ring, head_id);
-
 		id = DESC_ID(head_id + 1);
 		id_prev_wrap = DESC_ID_PREV_WRAP(desc_ring, id);
 
-- 
2.17.1

Re: [PATCH] printk: remove unneeded dead-store assignment

[Nathan Chancellor]

On Fri, Nov 06, 2020 at 04:40:05AM +0100, Lukas Bulwahn wrote:
> make clang-analyzer on x86_64 defconfig caught my attention with:
> 
>   kernel/printk/printk_ringbuffer.c:885:3: warning:
>   Value stored to 'desc' is never read [clang-analyzer-deadcode.DeadStores]
>                 desc = to_desc(desc_ring, head_id);
>                 ^
> 
> Commit b6cf8b3f3312 ("printk: add lockless ringbuffer") introduced
> desc_reserve() with this unneeded dead-store assignment.
> 
> As discussed with John Ogness privately, this is probably just some minor
> left-over from previous iterations of the ringbuffer implementation. So,
> simply remove this unneeded dead assignment to make clang-analyzer happy.
> 
> As compilers will detect this unneeded assignment and optimize this anyway,
> the resulting object code is identical before and after this change.
> 
> No functional change. No change to object code.
> 
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>

> ---
> applies cleanly on current master and next-20201105
> 
> John, please ack.
> Petr, please pick this minor non-urgent clean-up patch.
> 
>  kernel/printk/printk_ringbuffer.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
> index 6b1525685277..74e25a1704f2 100644
> --- a/kernel/printk/printk_ringbuffer.c
> +++ b/kernel/printk/printk_ringbuffer.c
> @@ -882,8 +882,6 @@ static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out)
>  	head_id = atomic_long_read(&desc_ring->head_id); /* LMM(desc_reserve:A) */
>  
>  	do {
> -		desc = to_desc(desc_ring, head_id);
> -
>  		id = DESC_ID(head_id + 1);
>  		id_prev_wrap = DESC_ID_PREV_WRAP(desc_ring, id);
>  
> -- 
> 2.17.1
> 

Re: [PATCH] printk: remove unneeded dead-store assignment

[Sergey Senozhatsky]

On (20/11/06 04:40), Lukas Bulwahn wrote:
> make clang-analyzer on x86_64 defconfig caught my attention with:
> 
>   kernel/printk/printk_ringbuffer.c:885:3: warning:
>   Value stored to 'desc' is never read [clang-analyzer-deadcode.DeadStores]
>                 desc = to_desc(desc_ring, head_id);
>                 ^
> 
> Commit b6cf8b3f3312 ("printk: add lockless ringbuffer") introduced
> desc_reserve() with this unneeded dead-store assignment.
> 
> As discussed with John Ogness privately, this is probably just some minor
> left-over from previous iterations of the ringbuffer implementation. So,
> simply remove this unneeded dead assignment to make clang-analyzer happy.
> 
> As compilers will detect this unneeded assignment and optimize this anyway,
> the resulting object code is identical before and after this change.
> 
> No functional change. No change to object code.
> 
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

	-ss

Re: [PATCH] printk: remove unneeded dead-store assignment

[John Ogness]

On 2020-11-06, Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote:
> make clang-analyzer on x86_64 defconfig caught my attention with:
>
>   kernel/printk/printk_ringbuffer.c:885:3: warning:
>   Value stored to 'desc' is never read [clang-analyzer-deadcode.DeadStores]
>                 desc = to_desc(desc_ring, head_id);
>                 ^
>
> Commit b6cf8b3f3312 ("printk: add lockless ringbuffer") introduced
> desc_reserve() with this unneeded dead-store assignment.
>
> As discussed with John Ogness privately, this is probably just some minor
> left-over from previous iterations of the ringbuffer implementation. So,
> simply remove this unneeded dead assignment to make clang-analyzer happy.
>
> As compilers will detect this unneeded assignment and optimize this anyway,
> the resulting object code is identical before and after this change.
>
> No functional change. No change to object code.
>
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>

Reviewed-by: John Ogness <john.ogness@linutronix.de>

Re: [PATCH] printk: remove unneeded dead-store assignment

[Petr Mladek]

On Fri 2020-11-06 04:40:05, Lukas Bulwahn wrote:
> make clang-analyzer on x86_64 defconfig caught my attention with:
> 
>   kernel/printk/printk_ringbuffer.c:885:3: warning:
>   Value stored to 'desc' is never read [clang-analyzer-deadcode.DeadStores]
>                 desc = to_desc(desc_ring, head_id);
>                 ^
> 
> Commit b6cf8b3f3312 ("printk: add lockless ringbuffer") introduced
> desc_reserve() with this unneeded dead-store assignment.
> 
> As discussed with John Ogness privately, this is probably just some minor
> left-over from previous iterations of the ringbuffer implementation. So,
> simply remove this unneeded dead assignment to make clang-analyzer happy.
> 
> As compilers will detect this unneeded assignment and optimize this anyway,
> the resulting object code is identical before and after this change.
> 
> No functional change. No change to object code.
> 
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>

The patch is committed in printk/linux.git, branch for-5.10-trivial.

It might still go into 5.10 when there is another important fix.
Otherwise, it would need to wait for 5.11 merge window.

Best Regards,
Petr