From 8e9bf8b9e8c0a3e1ef16dd48260a113f65ed01d2 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Mon, 26 Jan 2026 19:08:36 +0100 Subject: printk, vt, fbcon: Remove console_conditional_schedule() do_con_write(), fbcon_redraw.*() invoke console_conditional_schedule() which is a conditional scheduling point based on printk's internal variables console_may_schedule. It may only be used if the console lock is acquired for instance via console_lock() or console_trylock(). Prinkt sets the internal variable to 1 (and allows to schedule) if the console lock has been acquired via console_lock(). The trylock does not allow it. The console_conditional_schedule() invocation in do_con_write() is invoked shortly before console_unlock(). The console_conditional_schedule() invocation in fbcon_redraw.*() original from fbcon_scroll() / vt's con_scroll() which originate from a line feed. In console_unlock() the variable is set to 0 (forbids to schedule) and it tries to schedule while making progress printing. This is brand new compared to when console_conditional_schedule() was added in v2.4.9.11. In v2.6.38-rc3, console_unlock() (started its existence) iterated over all consoles and flushed them with disabled interrupts. A scheduling attempt here was not possible, it relied that a long print scheduled before console_unlock(). Since commit 8d91f8b15361d ("printk: do cond_resched() between lines while outputting to consoles"), which appeared in v4.5-rc1, console_unlock() attempts to schedule if it was allowed to schedule while during console_lock(). Each record is idealy one line so after every line feed. This console_conditional_schedule() is also only relevant on PREEMPT_NONE and PREEMPT_VOLUNTARY builds. In other configurations cond_resched() becomes a nop and has no impact. I'm bringing this all up just proof that it is not required anymore. It becomes a problem on a PREEMPT_RT build with debug code enabled because that might_sleep() in cond_resched() remains and triggers a warnings. This is due to legacy_kthread_func-> console_flush_one_record -> vt_console_print-> lf -> con_scroll -> fbcon_scroll and vt_console_print() acquires a spinlock_t which does not allow a voluntary schedule. There is no need to fb_scroll() to schedule since console_flush_one_record() attempts to schedule after each line. !PREEMPT_RT is not affected because the legacy printing thread is only enabled on PREEMPT_RT builds. Therefore I suggest to remove console_conditional_schedule(). Cc: Simona Vetter Cc: Helge Deller Cc: linux-fbdev@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Fixes: 5f53ca3ff83b4 ("printk: Implement legacy printer kthread for PREEMPT_RT") Signed-off-by: Sebastian Andrzej Siewior Acked-by: Greg Kroah-Hartman Acked-by: Petr Mladek # from printk() POV Signed-off-by: Helge Deller --- include/linux/console.h | 1 - 1 file changed, 1 deletion(-) (limited to 'include') diff --git a/include/linux/console.h b/include/linux/console.h index 1346f0b4cd8b..5520e4477ad7 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -697,7 +697,6 @@ extern int unregister_console(struct console *); extern void console_lock(void); extern int console_trylock(void); extern void console_unlock(void); -extern void console_conditional_schedule(void); extern void console_unblank(void); extern void console_flush_on_panic(enum con_flush_mode mode); extern struct tty_driver *console_device(int *); -- cgit v1.2.3