From 72d02adae32039da7eb8c63f062964b39b5b3147 Mon Sep 17 00:00:00 2001 From: Douglas Anderson Date: Tue, 22 Aug 2023 13:19:46 -0700 Subject: [PATCH] kgdb: Flush console before entering kgdb on panic [ Upstream commit dd712d3d45807db9fcae28a522deee85c1f2fde6 ] When entering kdb/kgdb on a kernel panic, it was be observed that the console isn't flushed before the `kdb` prompt came up. Specifically, when using the buddy lockup detector on arm64 and running: echo HARDLOCKUP > /sys/kernel/debug/provoke-crash/DIRECT I could see: [ 26.161099] lkdtm: Performing direct entry HARDLOCKUP [ 32.499881] watchdog: Watchdog detected hard LOCKUP on cpu 6 [ 32.552865] Sending NMI from CPU 5 to CPUs 6: [ 32.557359] NMI backtrace for cpu 6 ... [backtrace for cpu 6] ... [ 32.558353] NMI backtrace for cpu 5 ... [backtrace for cpu 5] ... [ 32.867471] Sending NMI from CPU 5 to CPUs 0-4,7: [ 32.872321] NMI backtrace forP cpuANC: Hard LOCKUP Entering kdb (current=..., pid 0) on processor 5 due to Keyboard Entry [5]kdb> As you can see, backtraces for the other CPUs start printing and get interleaved with the kdb PANIC print. Let's replicate the commands to flush the console in the kdb panic entry point to avoid this. Signed-off-by: Douglas Anderson Link: https://lore.kernel.org/r/20230822131945.1.I5b460ae8f954e4c4f628a373d6e74713c06dd26f@changeid Signed-off-by: Daniel Thompson Signed-off-by: Sasha Levin --- kernel/debug/debug_core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c index d5e9ccd..3a904d8 100644 --- a/kernel/debug/debug_core.c +++ b/kernel/debug/debug_core.c @@ -1006,6 +1006,9 @@ void kgdb_panic(const char *msg) if (panic_timeout) return; + debug_locks_off(); + console_flush_on_panic(CONSOLE_FLUSH_PENDING); + if (dbg_kdb_mode) kdb_printf("PANIC: %s\n", msg); -- 2.7.4