tree 9a4c2a8e61fd81b20c3f2ca9663f5aeecb594744
parent d2d786ddcbc2dec28cc252e57020f627c2bd2df3
author Barret Rhoden <brho@cs.berkeley.edu> 1531518230 -0400
committer Barret Rhoden <brho@cs.berkeley.edu> 1531518987 -0400

Serialize printing during panic()

When multiple cores panicked concurrently, their output would be garbled.
They also didn't have very useful info, and I almost always wanted a
backtrace.  Now we should get each core printing on its own, including a
backtrace.

The monitor() call needs to happen outside the lock, so we'll wait a little
till the other cores are likely done.  They just need to wait long enough
for another core to grab the lock and set 'panic_printing'.  500ms seems to
be enough, even on Qemu.

This is only lightly tested - crazy panics under insane conditions might
break a bit more than before.

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>