Patch "kgdb: Flush console before entering kgdb on panic" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    kgdb: Flush console before entering kgdb on panic

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kgdb-flush-console-before-entering-kgdb-on-panic.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit df76faaef0d40044571dbce1ad648d019d1302b1
Author: Douglas Anderson <dianders@xxxxxxxxxxxx>
Date:   Tue Aug 22 13:19:46 2023 -0700

    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 <dianders@xxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230822131945.1.I5b460ae8f954e4c4f628a373d6e74713c06dd26f@changeid
    Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 7beceb447211d..f40ca4f09afce 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -1018,6 +1018,9 @@ 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);