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Message-Id: <20250927-printk_legacy_thread_console_lock-v2-3-cff9f063071a@thegoodpenguin.co.uk>
Date: Sat, 27 Sep 2025 23:05:37 +0100
From: Andrew Murray <amurray@...goodpenguin.co.uk>
To: Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>,
John Ogness <john.ogness@...utronix.de>,
Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: linux-kernel@...r.kernel.org,
Andrew Murray <amurray@...goodpenguin.co.uk>
Subject: [PATCH v2 3/3] printk: Use console_flush_one_record for legacy
printer kthread
The legacy printer kthread uses console_lock and
__console_flush_and_unlock to flush records to the console. This
approach results in the console_lock being held for the entire
duration of a flush. This can result in large waiting times for
those waiting for console_lock especially where there is a large
volume of records or where the console is slow (e.g. serial). This
contention is observed during boot, as the call to filp_open in
console_on_rootfs will delay progression to userspace until any
in-flight flush is completed.
Let's instead use console_flush_one_record and release/reacquire
the console_lock between records.
On a PocketBeagle 2, with the following boot args:
"console=ttyS2,9600 initcall_debug=1 loglevel=10"
Without this patch:
[ 5.613166] +console_on_rootfs/filp_open
[ 5.643473] mmc1: SDHCI controller on fa00000.mmc [fa00000.mmc] using ADMA 64-bit
[ 5.643823] probe of fa00000.mmc returned 0 after 258244 usecs
[ 5.710520] mmc1: new UHS-I speed SDR104 SDHC card at address 5048
[ 5.721976] mmcblk1: mmc1:5048 SD32G 29.7 GiB
[ 5.747258] mmcblk1: p1 p2
[ 5.753324] probe of mmc1:5048 returned 0 after 40002 usecs
[ 15.595240] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to 30040000.pruss
[ 15.595282] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to e010000.watchdog
[ 15.595297] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to e000000.watchdog
[ 15.595437] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to 30300000.crc
[ 146.275961] -console_on_rootfs/filp_open ...
and with:
[ 5.477122] +console_on_rootfs/filp_open
[ 5.595814] mmc1: SDHCI controller on fa00000.mmc [fa00000.mmc] using ADMA 64-bit
[ 5.596181] probe of fa00000.mmc returned 0 after 312757 usecs
[ 5.662813] mmc1: new UHS-I speed SDR104 SDHC card at address 5048
[ 5.674367] mmcblk1: mmc1:5048 SD32G 29.7 GiB
[ 5.699320] mmcblk1: p1 p2
[ 5.705494] probe of mmc1:5048 returned 0 after 39987 usecs
[ 6.418682] -console_on_rootfs/filp_open ...
...
[ 15.593509] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to 30040000.pruss
[ 15.593551] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to e010000.watchdog
[ 15.593566] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to e000000.watchdog
[ 15.593704] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to 30300000.crc
Where I've added a printk surrounding the call in console_on_rootfs to filp_open.
Suggested-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Andrew Murray <amurray@...goodpenguin.co.uk>
---
kernel/printk/printk.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e2c1cacdb4164489c60fe38f1e2837eb838107d6..2c9b9383df76de956a05211537264fd6e06366da 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3668,17 +3668,29 @@ static bool legacy_kthread_should_wakeup(void)
static int legacy_kthread_func(void *unused)
{
- for (;;) {
- wait_event_interruptible(legacy_wait, legacy_kthread_should_wakeup());
+ bool any_progress;
+
+wait_for_event:
+ wait_event_interruptible(legacy_wait,
+ legacy_kthread_should_wakeup());
+
+ do {
+ bool any_usable;
+ bool handover = false;
+ u64 next_seq;
if (kthread_should_stop())
- break;
+ return 0;
console_lock();
- __console_flush_and_unlock();
- }
+ any_progress = console_flush_one_record(true, &next_seq,
+ &handover, &any_usable);
+ if (!handover)
+ __console_unlock();
- return 0;
+ } while (any_progress);
+
+ goto wait_for_event;
}
static bool legacy_kthread_create(void)
--
2.34.1
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