From: Andrew Murray Date: Mon, 20 Oct 2025 15:38:07 +0000 (+0100) Subject: printk: Use console_flush_one_record for legacy printer kthread X-Git-Url: https://gentwo.org/gitweb/?a=commitdiff_plain;h=1bc9a28f076fa68736603515dcf4ec027cb70102;p=linux%2F.git 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 Signed-off-by: Andrew Murray Reviewed-by: Petr Mladek Reviewed-by: John Ogness Link: https://patch.msgid.link/20251020-printk_legacy_thread_console_lock-v3-3-00f1f0ac055a@thegoodpenguin.co.uk [pmladek@suse.com: Fixed ordering of variable definition suggested by John.] Signed-off-by: Petr Mladek --- diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 60e39cfb2bc0..cb79d1d2e6e5 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3644,17 +3644,26 @@ 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 try_again; + +wait_for_event: + wait_event_interruptible(legacy_wait, legacy_kthread_should_wakeup()); + + do { + bool handover = false; + u64 next_seq = 0; if (kthread_should_stop()) - break; + return 0; console_lock(); - __console_flush_and_unlock(); - } + console_flush_one_record(true, &next_seq, &handover, &try_again); + if (!handover) + __console_unlock(); - return 0; + } while (try_again); + + goto wait_for_event; } static bool legacy_kthread_create(void)