+ mm-kmemleak-avoid-deadlock-by-moving-pr_warn-outside-kmemleak_lock.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/kmemleak: avoid deadlock by moving pr_warn() outside kmemleak_lock
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-kmemleak-avoid-deadlock-by-moving-pr_warn-outside-kmemleak_lock.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmemleak-avoid-deadlock-by-moving-pr_warn-outside-kmemleak_lock.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Breno Leitao <leitao@debian.org>
Subject: mm/kmemleak: avoid deadlock by moving pr_warn() outside kmemleak_lock
Date: Thu, 31 Jul 2025 02:57:18 -0700

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: c5665868183fec ("mm: kmemleak: use the memory pool for early allocations")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reported-by: Jakub Kicinski <kuba@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kmemleak.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/kmemleak.c~mm-kmemleak-avoid-deadlock-by-moving-pr_warn-outside-kmemleak_lock
+++ a/mm/kmemleak.c
@@ -470,6 +470,7 @@ static struct kmemleak_object *mem_pool_
 {
 	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_
 	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;
 }
_

Patches currently in -mm which might be from leitao@debian.org are

mm-kmemleak-avoid-deadlock-by-moving-pr_warn-outside-kmemleak_lock.patch