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Message-Id: <20250731-kmemleak_lock-v1-1-728fd470198f@debian.org>
Date: Thu, 31 Jul 2025 02:57:18 -0700
From: Breno Leitao <leitao@...ian.org>
To: Catalin Marinas <catalin.marinas@....com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
netdev@...r.kernel.org, kuba@...nel.org, stable@...rel.org,
kernel-team@...a.com, Breno Leitao <leitao@...ian.org>
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.
Reported-by: Jakub Kicinski <kuba@...nel.org>
Fixes: c5665868183fec ("mm: kmemleak: use the memory pool for early allocations")
Signed-off-by: Breno Leitao <leitao@...ian.org>
---
mm/kmemleak.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 8d588e6853110..e0333455c7384 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;
}
---
base-commit: 260f6f4fda93c8485c8037865c941b42b9cba5d2
change-id: 20250731-kmemleak_lock-4e04743ea79e
Best regards,
--
Breno Leitao <leitao@...ian.org>
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