On 2025-08-11, Marcos Paulo de Souza <mpdeso...@suse.com> wrote:
> These helpers will be used when calling console->write_atomic on
> KDB code in the next patch. It's basically the same implementaion
> as nbcon_device_try_acquire, but using NBCON_PORIO_EMERGENCY when
> acquiring the context.
>
> For release, differently from nbcon_device_release, we don't need to
> flush the console, since all CPUs are stopped when KDB is active.
>
> Signed-off-by: Marcos Paulo de Souza <mpdeso...@suse.com>
> ---
> include/linux/console.h | 6 ++++++
> kernel/printk/nbcon.c | 26 ++++++++++++++++++++++++++
> 2 files changed, 32 insertions(+)
>
> diff --git a/include/linux/console.h b/include/linux/console.h
> index
> 67af483574727c00eea1d5a1eacc994755c92607..b34c5a0b86303e2fb4583fa467d8be43761cf756
> 100644
> --- a/include/linux/console.h
> +++ b/include/linux/console.h
> @@ -605,6 +605,9 @@ extern bool nbcon_can_proceed(struct nbcon_write_context
> *wctxt);
> extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt);
> extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt);
> extern void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt);
> +extern bool nbcon_kdb_try_acquire(struct console *con,
> + struct nbcon_write_context *wctxt);
> +extern void nbcon_kdb_release(struct nbcon_write_context *wctxt);
>
> /*
> * Check if the given console is currently capable and allowed to print
> @@ -654,6 +657,9 @@ static inline bool nbcon_can_proceed(struct
> nbcon_write_context *wctxt) { return
> static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) {
> return false; }
> static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) {
> return false; }
> static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt)
> { }
> +static inline bool nbcon_kdb_try_acquire(struct console *con,
> + struct nbcon_write_context *wctxt) {
> return false; }
> +static inline void nbcon_kdb_release(struct console *con) { }
> static inline bool console_is_usable(struct console *con, short flags,
> bool use_atomic) { return false; }
> #endif
> diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
> index
> 646801813415f0abe40cabf2f28ca9e30664f028..79d8c7437806119ad9787ddc48382dc2c86c23c3
> 100644
> --- a/kernel/printk/nbcon.c
> +++ b/kernel/printk/nbcon.c
> @@ -1855,3 +1855,29 @@ void nbcon_device_release(struct console *con)
> console_srcu_read_unlock(cookie);
> }
> EXPORT_SYMBOL_GPL(nbcon_device_release);
> +
> +bool nbcon_kdb_try_acquire(struct console *con,
> + struct nbcon_write_context *wctxt)
> +{
> + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
> +
> + memset(ctxt, 0, sizeof(*ctxt));
> + ctxt->console = con;
> + ctxt->prio = NBCON_PRIO_EMERGENCY;
> +
> + if (!nbcon_context_try_acquire(ctxt, false))
> + return false;
> +
> + if (!nbcon_context_enter_unsafe(ctxt))
> + return false;
> +
> + return true;
> +}
> +
> +void nbcon_kdb_release(struct nbcon_write_context *wctxt)
> +{
> + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
> +
> + nbcon_context_exit_unsafe(ctxt);
> + nbcon_context_release(ctxt);
If nbcon_context_exit_unsafe() fails, the current task is no longer the
owner and thus a release is not needed. I would prefer:
if (nbcon_context_exit_unsafe(ctxt))
nbcon_context_release(ctxt);
or
if (!nbcon_context_exit_unsafe(ctxt))
return;
nbcon_context_release(ctxt);
You can find this same pattern in nbcon_device_release().
John
_______________________________________________
Kgdb-bugreport mailing list
Kgdb-bugreport@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
