FAILED: patch "[PATCH] mm/kmemleak: avoid deadlock by moving pr_warn() outside" failed to apply to 5.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x 47b0f6d8f0d2be4d311a49e13d2fd5f152f492b2
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025081848-proximity-feline-dfea@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 47b0f6d8f0d2be4d311a49e13d2fd5f152f492b2 Mon Sep 17 00:00:00 2001
From: Breno Leitao <leitao@debian.org>
Date: Thu, 31 Jul 2025 02:57:18 -0700
Subject: [PATCH] mm/kmemleak: avoid deadlock by moving pr_warn() outside
 kmemleak_lock

When netpoll is enabled, calling pr_warn_once() while holding
kmemleak_lock in mem_pool_alloc() can cause a deadlock due to lock
inversion with the netconsole subsystem.  This occurs because
pr_warn_once() may trigger netpoll, which eventually leads to
__alloc_skb() and back into kmemleak code, attempting to reacquire
kmemleak_lock.

This is the path for the deadlock.

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

Fix this by setting a flag and issuing the pr_warn_once() after
kmemleak_lock is released.

Link: https://lkml.kernel.org/r/20250731-kmemleak_lock-v1-1-728fd470198f@debian.org
Fixes: c5665868183f ("mm: kmemleak: use the memory pool for early allocations")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reported-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.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 8d588e685311..e0333455c738 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -470,6 +470,7 @@ static struct kmemleak_object *mem_pool_alloc(gfp_t gfp)
 {
 	unsigned long flags;
 	struct kmemleak_object *object;
+	bool warn = false;
 
 	/* try the slab allocator first */
 	if (object_cache) {
@@ -488,8 +489,10 @@ static struct kmemleak_object *mem_pool_alloc(gfp_t gfp)
 	else if (mem_pool_free_count)
 		object = &mem_pool[--mem_pool_free_count];
 	else
-		pr_warn_once("Memory pool empty, consider increasing CONFIG_DEBUG_KMEMLEAK_MEM_POOL_SIZE\n");
+		warn = true;
 	raw_spin_unlock_irqrestore(&kmemleak_lock, flags);
+	if (warn)
+		pr_warn_once("Memory pool empty, consider increasing CONFIG_DEBUG_KMEMLEAK_MEM_POOL_SIZE\n");
 
 	return object;
 }