Re: [PATCH] printk_ringbuffer: Avoid needless read of prb_desc

[wangwensheng <wsw9603@163.com>]

On 9/24/26 21:49, John Ogness wrote:
> On 2026-09-22, Wang Wensheng <wsw9603@163.com> wrote:
>> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
>> index 85c0c854b3ce..607666d37455 100644
>> --- a/kernel/printk/printk_ringbuffer.c
>> +++ b/kernel/printk/printk_ringbuffer.c
>> @@ -443,8 +443,8 @@ static enum desc_state get_desc_state(unsigned long id,
>>    * descriptor is in an inconsistent state (miss or reserved), the caller can
>>    * only expect the descriptor's @state_var field to be valid.
>>    *
>> - * The sequence number and caller_id can be optionally retrieved. Like all
>> - * non-state_var data, they are only valid if the descriptor is in a
>> + * The sequence number, caller_id, and desc can be optionally retrieved. Like
>> + * all non-state_var data, they are only valid if the descriptor is in a
>>    * consistent state.
>>    */
> I realize you are trying to minimally update the documentation. But
> really the whole description needs to be appropriately updated. I
> suggest:
>
> /*
>   * Get the state of a specified descriptor.
>   *
>   * Optionally, a copy of the descriptor, sequence number and/or caller ID can
>   * be retrieved. However, (with the exception of @desc_out->state_var) all
>   * retrieved values are invalid if the descriptor is in an inconsistent state
>   * (miss or reserved).
>   */
>
>>   static enum desc_state desc_read(struct prb_desc_ring *desc_ring,
>> @@ -1335,7 +1335,6 @@ static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring,
>>   {
>>   	unsigned long prev_state_val;
>>   	enum desc_state d_state;
>> -	struct prb_desc desc;
>>   	struct prb_desc *d;
>>   	unsigned long id;
>>   	u32 cid;
>> @@ -1346,7 +1345,7 @@ static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring,
>>   	 * To reduce unnecessarily reopening, first check if the descriptor
>>   	 * state and caller ID are correct.
>>   	 */
>> -	d_state = desc_read(desc_ring, id, &desc, NULL, &cid);
>> +	d_state = desc_read(desc_ring, id, NULL, NULL, &cid);
>>   	if (d_state != desc_committed || cid != caller_id)
>>   		return NULL;
>>   
>> @@ -2007,14 +2006,13 @@ u64 prb_first_seq(struct printk_ringbuffer *rb)
>>   {
>>   	struct prb_desc_ring *desc_ring = &rb->desc_ring;
>>   	enum desc_state d_state;
>> -	struct prb_desc desc;
>>   	unsigned long id;
>>   	u64 seq;
>>   
>>   	for (;;) {
>>   		id = atomic_long_read(&rb->desc_ring.tail_id); /* LMM(prb_first_seq:A) */
>>   
>> -		d_state = desc_read(desc_ring, id, &desc, &seq, NULL); /* LMM(prb_first_seq:B) */
>> +		d_state = desc_read(desc_ring, id, NULL, &seq, NULL); /* LMM(prb_first_seq:B) */
>>   
>>   		/*
>>   		 * This loop will not be infinite because the tail is
> Using my suggestion for the documentation:
>
> Reviewed-by: John Ogness <john.ogness@linutronix.de>
Thanks for your comment. I have sent a new patch with your suggestion.