linux-kernel - [PATCH 1/2] debugobjects: Warn wrong annotation outside bucket lock

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Message-Id: <20181213043447.23006-1-dima@arista.com>
Date:   Thu, 13 Dec 2018 04:34:46 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     0x7f454c46@...il.com, Dmitry Safonov <dima@...sta.com>,
        kernel test robot <rong.a.chen@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH 1/2] debugobjects: Warn wrong annotation outside bucket lock

debugobjects checks during initialization where the real object resides.
Kernel must use debug_object_init() or debug_object_init_on_stack()
accordingly. I'm not sure if it's worth to check debug_object
initialization place, but it seems to be well-documented.

If initialization function finds that the debug object actually resides
in a different place than was annotated, warning is being printed.

Unfortunately, it becomes error-prone to use WARN() or printing under
debugobjects bucket lock: printk() may defer work to workqueue, and
realization of workqueues uses debugobjects. Further, console drivers
use page allocator, potentially vmalloc() or slub/slab. Which reasonably
makes lockdep to go nuts as there are debug_check_no_obj_freed() checks
in allocators.

Move printings out of debugobjets bucket lock to address the potential
lockups.

Link: lkml.kernel.org/r/20181211091154.GL23332@...o2-debian
Reported-by: kernel test robot <rong.a.chen@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Waiman Long <longman@...hat.com>
Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
 lib/debugobjects.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 55437fd5128b..98968219405b 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -368,13 +368,14 @@ static void debug_object_is_on_stack(void *addr, int onstack)
 	WARN_ON(1);
 }
 
-static void
-__debug_object_init(void *addr, struct debug_obj_descr *descr, int onstack)
+static bool
+__debug_object_init(void *addr, struct debug_obj_descr *descr)
 {
 	enum debug_obj_state state;
 	struct debug_bucket *db;
 	struct debug_obj *obj;
 	unsigned long flags;
+	bool allocated = false;
 
 	fill_pool();
 
@@ -389,9 +390,9 @@ __debug_object_init(void *addr, struct debug_obj_descr *descr, int onstack)
 			debug_objects_enabled = 0;
 			raw_spin_unlock_irqrestore(&db->lock, flags);
 			debug_objects_oom();
-			return;
+			return false;
 		}
-		debug_object_is_on_stack(addr, onstack);
+		allocated = true;
 	}
 
 	switch (obj->state) {
@@ -406,7 +407,7 @@ __debug_object_init(void *addr, struct debug_obj_descr *descr, int onstack)
 		state = obj->state;
 		raw_spin_unlock_irqrestore(&db->lock, flags);
 		debug_object_fixup(descr->fixup_init, addr, state);
-		return;
+		return allocated;
 
 	case ODEBUG_STATE_DESTROYED:
 		debug_print_object(obj, "init");
@@ -416,6 +417,7 @@ __debug_object_init(void *addr, struct debug_obj_descr *descr, int onstack)
 	}
 
 	raw_spin_unlock_irqrestore(&db->lock, flags);
+	return allocated;
 }
 
 /**
@@ -428,7 +430,8 @@ void debug_object_init(void *addr, struct debug_obj_descr *descr)
 	if (!debug_objects_enabled)
 		return;
 
-	__debug_object_init(addr, descr, 0);
+	if (__debug_object_init(addr, descr))
+		debug_object_is_on_stack(addr, 0);
 }
 EXPORT_SYMBOL_GPL(debug_object_init);
 
@@ -443,7 +446,8 @@ void debug_object_init_on_stack(void *addr, struct debug_obj_descr *descr)
 	if (!debug_objects_enabled)
 		return;
 
-	__debug_object_init(addr, descr, 1);
+	if (__debug_object_init(addr, descr))
+		debug_object_is_on_stack(addr, 1);
 }
 EXPORT_SYMBOL_GPL(debug_object_init_on_stack);
 
-- 
2.20.0