[PATCH 6/7] dyndbg: add locking around zpool-add loop in zpool-init

From: Jim Cromie
Date: Fri Aug 07 2020 - 16:10:29 EST

This commit doesnt improve things, last commit was working, next one
still breaks, despite this "fix". I keep it separate for the
following review, which now stated, will be refuted as needed. ;-)

Locking review:

ddebug_zpool_init(), like other *_init() routines, does no locking
itself. Unlike them, it runs later, at late_init. This patch doesnt
fix the kernel panic that HEAD+1 does.

ddebug_callsite_get/put() are called as a pair under mutex-lock for
all 3 callsite users, 2: ddebug_change(), dynamic_emit_prefix(), do
their own ABBA-ish LGPU (Lock-Get-Put-Unlock).

ddebug_proc_show() does the GP part, and is wrapped by
ddebug_proc_start|stop() with LU.

ddebug_add_module() does LU to protect list_add(), HEAD~1 added
ddebug_zpool_add() loop inside that protection.

This commit adds locking to ddebug_zpool_init(), around the loop of
ddebug_zpool_add(), to match the locking in ddebug_add_module().

Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
lib/dynamic_debug.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index fdf52a26a504..701d3d1fb7e7 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -1182,8 +1182,10 @@ static void __init ddebug_zpool_init(void)

/* add-module normally does this, but not in time for builtins */
+ mutex_lock(&ddebug_lock);
for (iter = __start___dyndbg; iter < __stop___dyndbg; iter++)
+ mutex_unlock(&ddebug_lock);

v2pr_info("total pages: %lu compaction: %lu\n",
@@ -1280,4 +1282,3 @@ early_initcall(dynamic_debug_init);

/* Debugfs setup must be done later */