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.
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| @@ -1006,6 +1006,9 @@ void kgdb_panic(const char *msg) · 1005 unmodified lines | |||
| 1006 | if (panic_timeout) | 1006 | if (panic_timeout) |
| 1007 | return; | 1007 | return; |
| 1008 | 1008 | ||
| 1009 | debug_locks_off(); | ||
| 1010 | console_flush_on_panic(CONSOLE_FLUSH_PENDING); | ||
| 1011 | |||
| 1009 | if (dbg_kdb_mode) | 1012 | if (dbg_kdb_mode) |
| 1010 | kdb_printf("PANIC: %s\n", msg); | 1013 | kdb_printf("PANIC: %s\n", msg); |
| 1011 | 1014 | ||