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Message-ID:
<DB9PR04MB84297ECBB5E4E1DA0BD8B1B592CCA@DB9PR04MB8429.eurprd04.prod.outlook.com>
Date: Wed, 12 Nov 2025 05:00:05 +0000
From: Sherry Sun <sherry.sun@....com>
To: John Ogness <john.ogness@...utronix.de>, Petr Mladek <pmladek@...e.com>
CC: Sergey Senozhatsky <senozhatsky@...omium.org>, Steven Rostedt
<rostedt@...dmis.org>, Jacky Bai <ping.bai@....com>, Jon Hunter
<jonathanh@...dia.com>, Thierry Reding <thierry.reding@...il.com>, Derek
Barbosa <debarbos@...hat.com>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "stable@...r.kernel.org"
<stable@...r.kernel.org>
Subject: RE: [PATCH printk v1 1/1] printk: Avoid scheduling irq_work on
suspend
> -----Original Message-----
> From: John Ogness <john.ogness@...utronix.de>
> Sent: Tuesday, November 11, 2025 10:43 PM
> To: Petr Mladek <pmladek@...e.com>
> Cc: Sergey Senozhatsky <senozhatsky@...omium.org>; Steven Rostedt
> <rostedt@...dmis.org>; Sherry Sun <sherry.sun@....com>; Jacky Bai
> <ping.bai@....com>; Jon Hunter <jonathanh@...dia.com>; Thierry Reding
> <thierry.reding@...il.com>; Derek Barbosa <debarbos@...hat.com>; linux-
> kernel@...r.kernel.org; stable@...r.kernel.org
> Subject: [PATCH printk v1 1/1] printk: Avoid scheduling irq_work on suspend
>
> Allowing irq_work to be scheduled while trying to suspend has shown to
> cause problems as some architectures interpret the pending interrupts as a
> reason to not suspend. This became a problem for
> printk() with the introduction of NBCON consoles. With every
> printk() call, NBCON console printing kthreads are woken by queueing
> irq_work. This means that irq_work continues to be queued due to
> printk() calls late in the suspend procedure.
>
> Avoid this problem by preventing printk() from queueing irq_work once
> console suspending has begun. This applies to triggering NBCON and legacy
> deferred printing as well as klogd waiters.
>
> Since triggering of NBCON threaded printing relies on irq_work, the
> pr_flush() within console_suspend_all() is used to perform the final flushing
> before suspending consoles and blocking irq_work queueing.
> NBCON consoles that are not suspended (due to the usage of the
> "no_console_suspend" boot argument) transition to atomic flushing.
>
> Introduce a new global variable @console_offload_blocked to flag when
> irq_work queueing is to be avoided. The flag is used by
> printk_get_console_flush_type() to avoid allowing deferred printing and
> switch NBCON consoles to atomic flushing. It is also used by
> vprintk_emit() to avoid klogd waking.
>
> Cc: <stable@...r.kernel.org> # 6.13.x because no drivers in 6.12.x
> Fixes: 6b93bb41f6ea ("printk: Add non-BKL (nbcon) console basic
> infrastructure")
> Closes:
> https://lore.ke/
> rnel.org%2Flkml%2FDB9PR04MB8429E7DDF2D93C2695DE401D92C4A%40DB
> 9PR04MB8429.eurprd04.prod.outlook.com&data=05%7C02%7Csherry.sun%4
> 0nxp.com%7C70da522fd21f416f3d1708de2130affc%7C686ea1d3bc2b4c6fa92
> cd99c5c301635%7C0%7C0%7C638984690180001517%7CUnknown%7CTWFp
> bGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4z
> MiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=jzpzHfyW
> 0kCsvsUz4DgQqSdoNxedZF2rnT9gS%2FuBa7A%3D&reserved=0
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
For this patch, Tested-by: Sherry Sun <sherry.sun@....com>
Best Regards
Sherry
> ---
> kernel/printk/internal.h | 8 ++++---
> kernel/printk/printk.c | 51 ++++++++++++++++++++++++++++------------
> 2 files changed, 41 insertions(+), 18 deletions(-)
>
> diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index
> f72bbfa266d6c..b20929b7d71f5 100644
> --- a/kernel/printk/internal.h
> +++ b/kernel/printk/internal.h
> @@ -230,6 +230,8 @@ struct console_flush_type {
> bool legacy_offload;
> };
>
> +extern bool console_irqwork_blocked;
> +
> /*
> * Identify which console flushing methods should be used in the context of
> * the caller.
> @@ -241,7 +243,7 @@ static inline void printk_get_console_flush_type(struct
> console_flush_type *ft)
> switch (nbcon_get_default_prio()) {
> case NBCON_PRIO_NORMAL:
> if (have_nbcon_console && !have_boot_console) {
> - if (printk_kthreads_running)
> + if (printk_kthreads_running
> && !console_irqwork_blocked)
> ft->nbcon_offload = true;
> else
> ft->nbcon_atomic = true;
> @@ -251,7 +253,7 @@ static inline void printk_get_console_flush_type(struct
> console_flush_type *ft)
> if (have_legacy_console || have_boot_console) {
> if (!is_printk_legacy_deferred())
> ft->legacy_direct = true;
> - else
> + else if (!console_irqwork_blocked)
> ft->legacy_offload = true;
> }
> break;
> @@ -264,7 +266,7 @@ static inline void printk_get_console_flush_type(struct
> console_flush_type *ft)
> if (have_legacy_console || have_boot_console) {
> if (!is_printk_legacy_deferred())
> ft->legacy_direct = true;
> - else
> + else if (!console_irqwork_blocked)
> ft->legacy_offload = true;
> }
> break;
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index
> 5aee9ffb16b9a..94fc4a8662d4b 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -462,6 +462,9 @@ bool have_boot_console;
> /* See printk_legacy_allow_panic_sync() for details. */ bool
> legacy_allow_panic_sync;
>
> +/* Avoid using irq_work when suspending. */ bool
> +console_irqwork_blocked;
> +
> #ifdef CONFIG_PRINTK
> DECLARE_WAIT_QUEUE_HEAD(log_wait);
> static DECLARE_WAIT_QUEUE_HEAD(legacy_wait);
> @@ -2426,7 +2429,7 @@ asmlinkage int vprintk_emit(int facility, int level,
>
> if (ft.legacy_offload)
> defer_console_output();
> - else
> + else if (!console_irqwork_blocked)
> wake_up_klogd();
>
> return printed_len;
> @@ -2730,10 +2733,20 @@ void console_suspend_all(void) {
> struct console *con;
>
> + if (console_suspend_enabled)
> + pr_info("Suspending console(s) (use no_console_suspend to
> debug)\n");
> +
> + /*
> + * Flush any console backlog and then avoid queueing irq_work until
> + * console_resume_all(). Until then deferred printing is no longer
> + * triggered, NBCON consoles transition to atomic flushing, and
> + * any klogd waiters are not triggered.
> + */
> + pr_flush(1000, true);
> + console_irqwork_blocked = true;
> +
> if (!console_suspend_enabled)
> return;
> - pr_info("Suspending console(s) (use no_console_suspend to
> debug)\n");
> - pr_flush(1000, true);
>
> console_list_lock();
> for_each_console(con)
> @@ -2754,26 +2767,34 @@ void console_resume_all(void)
> struct console_flush_type ft;
> struct console *con;
>
> - if (!console_suspend_enabled)
> - return;
> -
> - console_list_lock();
> - for_each_console(con)
> - console_srcu_write_flags(con, con->flags &
> ~CON_SUSPENDED);
> - console_list_unlock();
> -
> /*
> - * Ensure that all SRCU list walks have completed. All printing
> - * contexts must be able to see they are no longer suspended so
> - * that they are guaranteed to wake up and resume printing.
> + * Allow queueing irq_work. After restoring console state, deferred
> + * printing and any klogd waiters need to be triggered in case there
> + * is now a console backlog.
> */
> - synchronize_srcu(&console_srcu);
> + console_irqwork_blocked = false;
> +
> + if (console_suspend_enabled) {
> + console_list_lock();
> + for_each_console(con)
> + console_srcu_write_flags(con, con->flags &
> ~CON_SUSPENDED);
> + console_list_unlock();
> +
> + /*
> + * Ensure that all SRCU list walks have completed. All printing
> + * contexts must be able to see they are no longer suspended
> so
> + * that they are guaranteed to wake up and resume printing.
> + */
> + synchronize_srcu(&console_srcu);
> + }
>
> printk_get_console_flush_type(&ft);
> if (ft.nbcon_offload)
> nbcon_kthreads_wake();
> if (ft.legacy_offload)
> defer_console_output();
> + else
> + wake_up_klogd();
>
> pr_flush(1000, true);
> }
> --
> 2.47.3
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