* Re: [PATCH] printk: remove unneeded dead-store assignment
2020-11-06 3:40 [PATCH] printk: remove unneeded dead-store assignment Lukas Bulwahn
@ 2020-11-06 3:49 ` Nathan Chancellor
2020-11-06 5:12 ` Sergey Senozhatsky
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Nathan Chancellor @ 2020-11-06 3:49 UTC (permalink / raw)
To: Lukas Bulwahn
Cc: Petr Mladek, Sergey Senozhatsky, Steven Rostedt, John Ogness,
Nick Desaulniers, linux-kernel, clang-built-linux,
kernel-janitors, linux-safety
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
>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] printk: remove unneeded dead-store assignment
2020-11-06 3:40 [PATCH] printk: remove unneeded dead-store assignment Lukas Bulwahn
2020-11-06 3:49 ` Nathan Chancellor
@ 2020-11-06 5:12 ` Sergey Senozhatsky
2020-11-06 8:18 ` John Ogness
2020-11-06 12:57 ` Petr Mladek
3 siblings, 0 replies; 5+ messages in thread
From: Sergey Senozhatsky @ 2020-11-06 5:12 UTC (permalink / raw)
To: Lukas Bulwahn
Cc: Petr Mladek, Sergey Senozhatsky, Steven Rostedt, John Ogness,
Nathan Chancellor, Nick Desaulniers, linux-kernel,
clang-built-linux, kernel-janitors, linux-safety
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
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] printk: remove unneeded dead-store assignment
2020-11-06 3:40 [PATCH] printk: remove unneeded dead-store assignment Lukas Bulwahn
2020-11-06 3:49 ` Nathan Chancellor
2020-11-06 5:12 ` Sergey Senozhatsky
@ 2020-11-06 8:18 ` John Ogness
2020-11-06 12:57 ` Petr Mladek
3 siblings, 0 replies; 5+ messages in thread
From: John Ogness @ 2020-11-06 8:18 UTC (permalink / raw)
To: Lukas Bulwahn, Petr Mladek, Sergey Senozhatsky, Steven Rostedt
Cc: Nathan Chancellor, Nick Desaulniers, linux-kernel,
clang-built-linux, kernel-janitors, linux-safety, Lukas Bulwahn
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>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] printk: remove unneeded dead-store assignment
2020-11-06 3:40 [PATCH] printk: remove unneeded dead-store assignment Lukas Bulwahn
` (2 preceding siblings ...)
2020-11-06 8:18 ` John Ogness
@ 2020-11-06 12:57 ` Petr Mladek
3 siblings, 0 replies; 5+ messages in thread
From: Petr Mladek @ 2020-11-06 12:57 UTC (permalink / raw)
To: Lukas Bulwahn
Cc: Sergey Senozhatsky, Steven Rostedt, John Ogness,
Nathan Chancellor, Nick Desaulniers, linux-kernel,
clang-built-linux, kernel-janitors, linux-safety
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
^ permalink raw reply [flat|nested] 5+ messages in thread