Commit c873ccbb authored by Gu Bowen's avatar Gu Bowen Committed by Andrew Morton
Browse files

mm: fix possible deadlock in kmemleak 

There are some AA deadlock issues in kmemleak, similar to the situation
reported by Breno [1].  The deadlock path is as follows:

mem_pool_alloc()
  -> raw_spin_lock_irqsave(&kmemleak_lock, flags);
      -> pr_warn()
          -> netconsole subsystem
	     -> netpoll
	         -> __alloc_skb
		   -> __create_object
		     -> raw_spin_lock_irqsave(&kmemleak_lock, flags);

To solve this problem, switch to printk_safe mode before printing warning
message, this will redirect all printk()-s to a special per-CPU buffer,
which will be flushed later from a safe context (irq work), and this
deadlock problem can be avoided.  The proper API to use should be
printk_deferred_enter()/printk_deferred_exit() [2].  Another way is to
place the warn print after kmemleak is released.

Link: https://lkml.kernel.org/r/20250822073541.1886469-1-gubowen5@huawei.com
Link: https://lore.kernel.org/all/20250731-kmemleak_lock-v1-1-728fd470198f@debian.org/#t [1]
Link: https://lore.kernel.org/all/5ca375cd-4a20-4807-b897-68b289626550@redhat.com/

 [2]
Signed-off-by: default avatarGu Bowen <gubowen5@huawei.com>
Reviewed-by: default avatarWaiman Long <longman@redhat.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Reviewed-by: default avatarBreno Leitao <leitao@debian.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Lu Jialin <lujialin4@huawei.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 6659d027

mm/kmemleak.c

+20 −7
Original line number Diff line number Diff line
@@ -437,9 +437,15 @@ static struct kmemleak_object *__lookup_object(unsigned long ptr, int alias, 
		else if (untagged_objp == untagged_ptr || alias)

			return object;

		else {

			/*

			 * Printk deferring due to the kmemleak_lock held.

			 * This is done to avoid deadlock.

			 */

			printk_deferred_enter();

			kmemleak_warn("Found object by alias at 0x%08lx\n",

				      ptr);

			dump_object_info(object);

			printk_deferred_exit();

			break;

		}

	}
@@ -736,6 +742,11 @@ static int __link_object(struct kmemleak_object *object, unsigned long ptr, 
		else if (untagged_objp + parent->size <= untagged_ptr)

			link = &parent->rb_node.rb_right;

		else {

			/*

			 * Printk deferring due to the kmemleak_lock held.

			 * This is done to avoid deadlock.

			 */

			printk_deferred_enter();

			kmemleak_stop("Cannot insert 0x%lx into the object search tree (overlaps existing)\n",

				      ptr);

			/*
@@ -743,6 +754,7 @@ static int __link_object(struct kmemleak_object *object, unsigned long ptr, 
			 * be freed while the kmemleak_lock is held.

			 */

			dump_object_info(parent);

			printk_deferred_exit();

			return -EEXIST;

		}

	}
@@ -856,13 +868,8 @@ static void delete_object_part(unsigned long ptr, size_t size, 


	raw_spin_lock_irqsave(&kmemleak_lock, flags);

	object = __find_and_remove_object(ptr, 1, objflags);

	if (!object) {

#ifdef DEBUG

		kmemleak_warn("Partially freeing unknown object at 0x%08lx (size %zu)\n",

			      ptr, size);

#endif

	if (!object)

		goto unlock;

	}



	/*

	 * Create one or two objects that may result from the memory block
@@ -882,8 +889,14 @@ static void delete_object_part(unsigned long ptr, size_t size, 


unlock:

	raw_spin_unlock_irqrestore(&kmemleak_lock, flags);

	if (object)

	if (object) {

		__delete_object(object);

	} else {

#ifdef DEBUG

		kmemleak_warn("Partially freeing unknown object at 0x%08lx (size %zu)\n",

			      ptr, size);

#endif

	}



out:

	if (object_l)