[PATCH v6 0/4] kdb: Improve console handling

From: Sumit Garg
Date: Thu Jun 04 2020 - 06:01:49 EST

This patch-set is aimed to improve console handling especially when kdb
operates in NMI context.

Brief description of enhancements:
- Add status check for console prior to invoking corresponding handler.
- Fixup to avoid possible deadlock in NMI context due to usage of locks
in the console handlers.
- Prefer usage of polling I/O driver mode (lockless APIs) over invocation
of console handlers.

Changes in v6:
- Replace early_con -> kgdboc_earlycon_io_ops.cons.
- Added Petr's review tag on patch #1, #2 and #3.
- Drop Doug's review tag from patch #4 due to early_con changes which I
think needs a re-review.

Changes in v5:
- Rebased on top of tags/kgdb-5.8-rc1.
- Get rid of kdb_io_write().
- Fixed issue reported by kbuild test robot.
- Remove is_console from kgdboc_earlycon_io_ops as well.
- Misc. comments.
- Added Doug's review tag.

Changes in v4:
- Use dbg_io_ops->write_char() directly instead of passing it as a
function pointer.
- Use "struct console" rather than "struct tty_driver" for comparison.
- Make commit descriptions and comments more informative.
- Add review tag for patch #2.

Changes in v3:
- Split patch to have separate patch for console status check.
- New patch to re-factor kdb message emit code.
- New patch to prefer polling I/O over console mode.
- Add code comments to describe usage of oops_in_progress.

Changes in v2:
- Use oops_in_progress directly instead of bust_spinlocks().

Sumit Garg (4):
kdb: Re-factor kdb_printf() message write code
kdb: Check status of console prior to invoking handlers
kdb: Make kdb_printf() console handling more robust
kdb: Switch to use safer dbg_io_ops over console APIs

drivers/tty/serial/kgdb_nmi.c | 2 +-
drivers/tty/serial/kgdboc.c | 32 +++++++++----------
drivers/usb/early/ehci-dbgp.c | 3 +-
include/linux/kgdb.h | 5 ++-
kernel/debug/kdb/kdb_io.c | 72 ++++++++++++++++++++++++++-----------------
5 files changed, 64 insertions(+), 50 deletions(-)