From 2a78b85b70f9c3d450619d369d349ba861320510 Mon Sep 17 00:00:00 2001 From: Sumit Garg Date: Thu, 4 Jun 2020 15:31:18 +0530 Subject: kdb: Make kdb_printf() console handling more robust While rounding up CPUs via NMIs, its possible that a rounded up CPU maybe holding a console port lock leading to kgdb master CPU stuck in a deadlock during invocation of console write operations. A similar deadlock could also be possible while using synchronous breakpoints. So in order to avoid such a deadlock, set oops_in_progress to encourage the console drivers to disregard their internal spin locks: in the current calling context the risk of deadlock is a bigger problem than risks due to re-entering the console driver. We operate directly on oops_in_progress rather than using bust_spinlocks() because the calls bust_spinlocks() makes on exit are not appropriate for this calling context. Suggested-by: Sergey Senozhatsky Signed-off-by: Sumit Garg Reviewed-by: Douglas Anderson Reviewed-by: Petr Mladek Link: https://lore.kernel.org/r/1591264879-25920-4-git-send-email-sumit.garg@linaro.org Signed-off-by: Daniel Thompson --- kernel/debug/kdb/kdb_io.c | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'kernel/debug') diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c index 58b7d256d0a4..0e4f2eda96d8 100644 --- a/kernel/debug/kdb/kdb_io.c +++ b/kernel/debug/kdb/kdb_io.c @@ -562,7 +562,18 @@ static void kdb_msg_write(const char *msg, int msg_len) for_each_console(c) { if (!(c->flags & CON_ENABLED)) continue; + /* + * Set oops_in_progress to encourage the console drivers to + * disregard their internal spin locks: in the current calling + * context the risk of deadlock is a bigger problem than risks + * due to re-entering the console driver. We operate directly on + * oops_in_progress rather than using bust_spinlocks() because + * the calls bust_spinlocks() makes on exit are not appropriate + * for this calling context. + */ + ++oops_in_progress; c->write(c, msg, msg_len); + --oops_in_progress; touch_nmi_watchdog(); } } -- cgit v1.2.3