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.or... 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; }