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

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Message-Id: <20200807200957.1269454-7-jim.cromie@gmail.com>
Date:   Fri,  7 Aug 2020 14:09:53 -0600
From:   Jim Cromie <jim.cromie@...il.com>
To:     jbaron@...mai.com, linux-kernel@...r.kernel.org
Cc:     Jim Cromie <jim.cromie@...il.com>
Subject: [PATCH 6/7] dyndbg: add locking around zpool-add loop in zpool-init

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@...il.com>
---
 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++)
 		ddebug_zpool_add(iter);
+	mutex_unlock(&ddebug_lock);

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

 /* Debugfs setup must be done later */
 fs_initcall(dynamic_debug_init_control);
-
-- 
2.26.2