Petr Mladek 9bd18e1262 printk/nbcon: Restore IRQ in atomic flush after each emitted record ... The commit d5d399efff ("printk/nbcon: Release nbcon consoles ownership in atomic flush after each emitted record") prevented stall of a CPU which lost nbcon console ownership because another CPU entered an emergency flush. But there is still the problem that the CPU doing the emergency flush might cause a stall on its own. Let's go even further and restore IRQ in the atomic flush after each emitted record. It is not a complete solution. The interrupts and/or scheduling might still be blocked when the emergency atomic flush was called with IRQs and/or scheduling disabled. But it should remove the following lockup: mlx5_core 0000:03:00.0: Shutdown was called kvm: exiting hardware virtualization arm-smmu-v3 arm-smmu-v3.10.auto: CMD_SYNC timeout at 0x00000103 [hwprod 0x00000104, hwcons 0x00000102] smp: csd: Detected non-responsive CSD lock (#1) on CPU#4, waiting 5000000032 ns for CPU#00 do_nothing (kernel/smp.c:1057) smp: csd: CSD lock (#1) unresponsive. [...] Call trace: pl011_console_write_atomic (./arch/arm64/include/asm/vdso/processor.h:12 drivers/tty/serial/amba-pl011.c:2540) (P) nbcon_emit_next_record (kernel/printk/nbcon.c:1049) __nbcon_atomic_flush_pending_con (kernel/printk/nbcon.c:1517) __nbcon_atomic_flush_pending.llvm.15488114865160659019 (./arch/arm64/include/asm/alternative-macros.h:254 ./arch/arm64/include/asm/cpufeature.h:808 ./arch/arm64/include/asm/irqflags.h:192 kernel/printk/nbcon.c:1562 kernel/printk/nbcon.c:1612) nbcon_atomic_flush_pending (kernel/printk/nbcon.c:1629) printk_kthreads_shutdown (kernel/printk/printk.c:?) syscore_shutdown (drivers/base/syscore.c:120) kernel_kexec (kernel/kexec_core.c:1045) __arm64_sys_reboot (kernel/reboot.c:794 kernel/reboot.c:722 kernel/reboot.c:722) invoke_syscall (arch/arm64/kernel/syscall.c:50) el0_svc_common.llvm.14158405452757855239 (arch/arm64/kernel/syscall.c:?) do_el0_svc (arch/arm64/kernel/syscall.c:152) el0_svc (./arch/arm64/include/asm/alternative-macros.h:254 ./arch/arm64/include/asm/cpufeature.h:808 ./arch/arm64/include/asm/irqflags.h:73 arch/arm64/kernel/entry-common.c:169 arch/arm64/kernel/entry-common.c:182 arch/arm64/kernel/entry-common.c:749) el0t_64_sync_handler (arch/arm64/kernel/entry-common.c:820) el0t_64_sync (arch/arm64/kernel/entry.S:600) In this case, nbcon_atomic_flush_pending() is called from printk_kthreads_shutdown() with IRQs and scheduling enabled. Note that __nbcon_atomic_flush_pending_con() is directly called also from nbcon_device_release() where the disabled IRQs might break PREEMPT_RT guarantees. But the atomic flush is called only in emergency or panic situations where the latencies are irrelevant anyway. An ultimate solution would be a touching of watchdogs. But it would hide all problems. Let's do it later when anyone reports a stall which does not have a better solution. Closes: https://lore.kernel.org/r/sqwajvt7utnt463tzxgwu2yctyn5m6bjwrslsnupfexeml6hkd@v6sqmpbu3vvu Tested-by: Breno Leitao <leitao@debian.org> Reviewed-by: John Ogness <john.ogness@linutronix.de> Link: https://patch.msgid.link/20251212124520.244483-1-pmladek@suse.com Signed-off-by: Petr Mladek <pmladek@suse.com>		2025-12-15 16:18:41 +01:00
..
.kunitconfig	printk: ringbuffer: Add KUnit test	2025-06-18 16:42:42 +02:00
braille.c	printk: Replace strncmp() with str_has_prefix()	2019-08-16 09:54:08 +02:00
braille.h	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
console_cmdline.h	printk: Add match_devname_and_update_preferred_console()	2024-07-04 15:41:44 +02:00
index.c	kernel/printk/index.c: fix memory leak with using debugfs_lookup()	2023-02-03 10:42:02 +01:00
internal.h	Merge branch 'rework/suspend-fixes' into for-linus	2025-12-01 14:16:28 +01:00
Makefile	printk: ringbuffer: Add KUnit test	2025-06-18 16:42:42 +02:00
nbcon.c	printk/nbcon: Restore IRQ in atomic flush after each emitted record	2025-12-15 16:18:41 +01:00
printk.c	Merge branch 'rework/threaded-printk' into for-linus	2025-12-01 14:16:45 +01:00
printk_ringbuffer.c	printk_ringbuffer: Create a helper function to decide whether more space is needed	2025-11-10 13:09:43 +01:00
printk_ringbuffer.h	printk: nbcon: Init @nbcon_seq to highest possible	2024-09-04 15:56:32 +02:00
printk_ringbuffer_kunit_test.c	printk: kunit: support offstack cpumask	2025-09-10 17:18:37 +02:00
printk_safe.c	printk: Defer legacy printing when holding printk_cpu_sync	2024-12-16 13:26:31 +01:00
sysctl.c	treewide: const qualify ctl_tables where applicable	2025-01-28 13:48:37 +01:00