[PATCH] lockdep: Introduce CONFIG_LOCKDEP_LARGE

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	syzbot <syzbot+62ebe501c1ce9a91f68c@syzkaller.appspotmail.com>,
	syzbot <syzbot+91fd909b6e62ebe06131@syzkaller.appspotmail.com>,
	syzbot <syzbot+cd0ec5211ac07c18c049@syzkaller.appspotmail.com>
Subject: [PATCH] lockdep: Introduce CONFIG_LOCKDEP_LARGE
Date: Sat, 25 Jul 2020 10:30:39 +0900	[thread overview]
Message-ID: <1595640639-9310-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> (raw)

Since syzkaller continues various test cases until the kernel crashes,
syzkaller tends to examine more locking dependencies than normal systems.
As a result, syzbot is reporting that the fuzz testing was terminated
due to hitting upper limits lockdep can track [1] [2] [3].

Like CONFIG_LOCKDEP_SMALL which halves the upper limits, let's introduce
CONFIG_LOCKDEP_LARGE which doubles the upper limits.

[1] https://syzkaller.appspot.com/bug?id=3d97ba93fb3566000c1c59691ea427370d33ea1b
[2] https://syzkaller.appspot.com/bug?id=381cb436fe60dc03d7fd2a092b46d7f09542a72a
[3] https://syzkaller.appspot.com/bug?id=a588183ac34c1437fc0785e8f220e88282e5a29f

Reported-by: syzbot <syzbot+cd0ec5211ac07c18c049@syzkaller.appspotmail.com>
Reported-by: syzbot <syzbot+91fd909b6e62ebe06131@syzkaller.appspotmail.com>
Reported-by: syzbot <syzbot+62ebe501c1ce9a91f68c@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 kernel/locking/lockdep.c           | 4 ++++
 kernel/locking/lockdep_internals.h | 5 +++++
 lib/Kconfig.debug                  | 8 ++++++++
 3 files changed, 17 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 29a8de4..85ba7eb 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1349,7 +1349,11 @@ static int add_lock_to_list(struct lock_class *this,
 /*
  * For good efficiency of modular, we use power of 2
  */
+#ifdef CONFIG_LOCKDEP_LARGE
+#define MAX_CIRCULAR_QUEUE_SIZE		8192UL
+#else
 #define MAX_CIRCULAR_QUEUE_SIZE		4096UL
+#endif
 #define CQ_MASK				(MAX_CIRCULAR_QUEUE_SIZE-1)
 
 /*
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index baca699..00a3ec3 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -93,6 +93,11 @@ enum {
 #define MAX_LOCKDEP_CHAINS_BITS	15
 #define MAX_STACK_TRACE_ENTRIES	262144UL
 #define STACK_TRACE_HASH_SIZE	8192
+#elif defined(CONFIG_LOCKDEP_LARGE)
+#define MAX_LOCKDEP_ENTRIES	65536UL
+#define MAX_LOCKDEP_CHAINS_BITS	17
+#define MAX_STACK_TRACE_ENTRIES	1048576UL
+#define STACK_TRACE_HASH_SIZE	32768
 #else
 #define MAX_LOCKDEP_ENTRIES	32768UL
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 9ad9210..69ba624 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1266,6 +1266,14 @@ config LOCKDEP
 config LOCKDEP_SMALL
 	bool
 
+config LOCKDEP_LARGE
+	bool "Use larger buffer for tracking more locking dependencies"
+	depends on LOCKDEP && !LOCKDEP_SMALL
+	help
+	  If you say Y here, the upper limits the lock dependency engine uses will
+	  be doubled. Useful for fuzz testing which tends to test many complecated
+	  dependencies than normal systems.
+
 config DEBUG_LOCKDEP
 	bool "Lock dependency engine debugging"
 	depends on DEBUG_KERNEL && LOCKDEP
-- 
1.8.3.1

