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
Link: https://lore.kernel.org/all/5ca375cd-4a20-4807-b897-68b289626550@redhat.com/
Signed-off-by: Gu Bowen <gubowen5@huawei.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Breno 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: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 84265983f239c19b3c361490dd28d2c68af1aa0b..1ac56ceb29b6b1baa613cf746e7b23a5d364571c 100644 (file)
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -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)