On Wed 19-04-23 09:42:10, Petr Mladek wrote:
> The comment above printk_deferred_enter()/exit() definition claims
> that it can be used only when interrupts are disabled.
>
> It was required by the original printk_safe_log_store() implementation.
> The code provided lockless synchronization between a single writer and
> a single reader. The interrupt and the normal context shared the same
> buffer.
>
> The commit 93d102f094be ("printk: remove safe buffers") removed
> these temporary buffers. Instead, the messages are stored directly into
> the new global lockless buffer which supports multiple parallel writers.
>
> As a result, it is safe to interrupt one writer now. The preemption still
> has to be disabled because the deferred context is CPU specific.
Thanks for the clarification and explanation.
> Fixes: 93d102f094be ("printk: remove safe buffers")
Is this a fix though? I would expect some users to be changed from irq
to preempt to disabling to be considered a fix.
> Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
> ---
> include/linux/printk.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index 8ef499ab3c1e..915a321b491e 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -161,7 +161,7 @@ extern void __printk_safe_enter(void);
> extern void __printk_safe_exit(void);
> /*
> * The printk_deferred_enter/exit macros are available only as a hack for
> - * some code paths that need to defer all printk console printing. Interrupts
> + * some code paths that need to defer all printk console printing. Preemption
> * must be disabled for the deferred duration.
> */
> #define printk_deferred_enter __printk_safe_enter
> --
> 2.35.3
--
Michal Hocko
SUSE Labs
