Until now unsafe flushing is only performed at the very end of panic(), before entering the infinite loop. For other situations (such as panic-kexec or panic-reboot or emergency-reboot) no unsafe flushing is performed. The reasoning for this is because an unsafe flush could lead to fireworks, which could prevent the kexec or reboot from occurring.
However, some users may be willing to take on such risks in order to see panic output. Indeed, for the netconsole (which does not support safe atomic printing) it is a regression that such unsafe printing does not occur. [0] This series adds unsafe flushing policy flags per-console to allow individual consoles to perform unsafe flushing for such scenarios. The unsafe flushing is hard-code-enabled for the netconsole in patch 6/6. The justification is that this is not less safe than the legacy netconsole. Later these policy flags could be easily exposed to userspace via /sys/class/consoles/, once the sysfs per-console interface is available. John Ogness [0] https://lore.kernel.org/lkml/[email protected] John Ogness (6): printk: Introduce and specify flush reasons console: Introduce unsafe flush policy flags printk: Evaluate flush policy in nbcon_allow_unsafe_takeover() printk: Remove nbcon_atomic_flush_unsafe() printk: Add panic+kexec flush point netconsole: Always perform unsafe flushing on panic/kdb/restart arch/powerpc/kernel/watchdog.c | 2 +- drivers/net/netconsole.c | 4 ++ include/linux/console.h | 37 ++++++++--- include/linux/printk.h | 27 ++++++-- kernel/crash_core.c | 1 + kernel/panic.c | 2 +- kernel/printk/internal.h | 4 +- kernel/printk/nbcon.c | 117 ++++++++++++++++++++++----------- kernel/printk/printk.c | 16 ++--- kernel/reboot.c | 2 +- lib/nmi_backtrace.c | 2 +- 11 files changed, 146 insertions(+), 68 deletions(-) base-commit: d01f86a7da8161aac8c6304b377cf58fb75861ca -- 2.47.3
