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From:   Qian Cai <cai@lca.pw>
To:     akpm@linux-foundation.org
Cc:     cl@linux.com, penberg@kernel.org, rientjes@google.com,
        iamjoonsoo.kim@lge.com, catalin.marinas@arm.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Qian Cai <cai@lca.pw>
Subject: [RESEND PATCH] slab: skip kmemleak_object in leaks_show()
Date:   Tue, 14 May 2019 10:47:41 -0400
Message-Id: <20190514144741.39460-1-cai@lca.pw>
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Sender: linux-kernel-owner@vger.kernel.org
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Running tests on a debug kernel will usually generate a large number of
kmemleak objects.

  # grep kmemleak /proc/slabinfo
  kmemleak_object   2243606 3436210 ...

As the result, reading /proc/slab_allocators could easily loop forever
while processing the kmemleak_object cache and any additional freeing or
allocating objects will trigger a reprocessing. To make a situation
worse, soft-lockups could easily happen in this sitatuion which will
call printk() to allocate more kmemleak objects to guarantee a livelock.

Since kmemleak_object has a single call site (create_object()), there
isn't much new information compared with slabinfo. Just skip it.

Signed-off-by: Qian Cai <cai@lca.pw>
---
 mm/slab.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/slab.c b/mm/slab.c
index 20f318f4f56e..85d1d223f879 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4285,6 +4285,15 @@ static int leaks_show(struct seq_file *m, void *p)
 	if (!(cachep->flags & SLAB_RED_ZONE))
 		return 0;
 
+	/*
+	 * /proc/slabinfo has the same information, so skip kmemleak here due to
+	 * a high volume and its RCU free could make cachep->store_user_clean
+	 * dirty all the time.
+	 */
+	if (IS_ENABLED(CONFIG_DEBUG_KMEMLEAK) &&
+	    !strcmp("kmemleak_object", cachep->name))
+		return 0;
+
 	/*
 	 * Set store_user_clean and start to grab stored user information
 	 * for all objects on this cache. If some alloc/free requests comes
-- 
2.20.1 (Apple Git-117)