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SubjectRe: [PATCH next v3 3/3] printk: remove logbuf_lock protection for ringbuffer
On (20/12/07 23:26), John Ogness wrote:
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index e1f068677a74..f3c0fcc3163f 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1068,7 +1068,6 @@ void __init setup_log_buf(int early)
> struct printk_record r;
> size_t new_descs_size;
> size_t new_infos_size;
> - unsigned long flags;
> char *new_log_buf;
> unsigned int free;
> u64 seq;
> @@ -1126,8 +1125,6 @@ void __init setup_log_buf(int early)
> new_descs, ilog2(new_descs_count),
> new_infos);
>
> - logbuf_lock_irqsave(flags);
> -
> log_buf_len = new_log_buf_len;
> log_buf = new_log_buf;
> new_log_buf_len = 0;
> @@ -1143,8 +1140,6 @@ void __init setup_log_buf(int early)
> */
> prb = &printk_rb_dynamic;
>
> - logbuf_unlock_irqrestore(flags);

logbuf_lock_irqsave() does two things - it locks the logbuf lock and
enables the printk_safe gating. While we can drop the former, the
latter one must stay until we have a complete replacement.

Looking more:

> ---
> logbuf_lock_irqsave(flags);
>
> log_buf_len = new_log_buf_len;
> log_buf = new_log_buf;
> new_log_buf_len = 0;
>
> free = __LOG_BUF_LEN;
> prb_for_each_record(0, &printk_rb_static, seq, &r)
> free -= add_to_rb(&printk_rb_dynamic, &r);
>
> /*
> * This is early enough that everything is still running on the
> * boot CPU and interrupts are disabled. So no new messages will
> * appear during the transition to the dynamic buffer.
> */
> prb = &printk_rb_dynamic;
>
> logbuf_unlock_irqrestore(flags);
---

I'd say that I'd prefer to keep logbuf initialisation under printk_safe(),
per-CPU buffer can be already initialised at this point. Strictly speaking
we can have new message during transition to the dynamic buffer - there are
functions there that can pr_err/warn while we prb_for_each_record/add_to_rb.

> -ss

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