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From: Boqun Feng <boqun.feng@gmail.com>
To: linux-kernel@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Andrea Parri <parri.andrea@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Boqun Feng <boqun.feng@gmail.com>
Subject: [RFC tip/locking/lockdep v6 06/20] lockdep: Introduce lock_list::dep
Date: Wed, 11 Apr 2018 21:50:56 +0800	[thread overview]
Message-ID: <20180411135110.9217-7-boqun.feng@gmail.com> (raw)
In-Reply-To: <20180411135110.9217-1-boqun.feng@gmail.com>

To add recursive read locks into the dependency graph, we need to store
the types of dependencies for the BFS later. There are four types of
dependencies:

*	Non-recursive -> Non-recursive dependencies: NN
	e.g. write_lock(prev) held and try to acquire write_lock(next),
	which can be represented as "prev -(NN)-> next".

*	Recursive -> Non-recursive dependencies: RN
	e.g. read_lock(prev) held and try to acquire write_lock(next),
	which can be represented as "prev -(RN)-> next".

*	Non-recursive -> recursive dependencies: NR
	e.g. write_lock(prev) held and try to acquire read_lock(next),
	which can be represented as "prev -(NR)-> next".

*	Recursive -> recursive dependencies: RR
	e.g. read_lock(prev) held and try to acquire read_lock(next),
	which can be represented as "prev -(RR)-> next".

So we use 4 bits for the presence of each type in lock_list::dep. Helper
functions and marcos are also introduced to convert a pair of locks into
lock_list::dep bit and maintain the addition of different types of
dependencies.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 include/linux/lockdep.h  |  2 ++
 kernel/locking/lockdep.c | 76 +++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 74 insertions(+), 4 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index d2af32387aaa..cbd257f62877 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -187,6 +187,8 @@ struct lock_list {
 	struct lock_class		*class;
 	struct stack_trace		trace;
 	u16				distance;
+	/* bitmap of different dependencies from head to this */
+	u8				dep;
 
 	/*
 	 * The parent field is used to implement breadth-first search, and the
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 1806060c88ce..0892855b6c57 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -859,7 +859,7 @@ static struct lock_list *alloc_list_entry(void)
  * Add a new dependency to the head of the list:
  */
 static int add_lock_to_list(struct lock_class *this, struct list_head *head,
-			    unsigned long ip, u16 distance,
+			    unsigned long ip, u16 distance, u8 dep,
 			    struct stack_trace *trace)
 {
 	struct lock_list *entry;
@@ -872,6 +872,7 @@ static int add_lock_to_list(struct lock_class *this, struct list_head *head,
 		return 0;
 
 	entry->class = this;
+	entry->dep = dep;
 	entry->distance = distance;
 	entry->trace = *trace;
 	/*
@@ -1012,6 +1013,41 @@ static inline bool bfs_error(enum bfs_result res)
 	return res < 0;
 }
 
+/*
+ * DEP_*_BIT in lock_list::dep
+ *
+ * For dependency @prev -> @next:
+ *
+ *   RR: both @prev and @next are recursive read locks, i.e. ->read == 2.
+ *   NR: @prev is a non-recursive and @next is recursive.
+ *   RN: @prev is recursive and @next is non-recursive.
+ *   NN: both @prev and @next are non-recursive.
+ *
+ * Note that we define the value of DEP_*_BITs so that:
+ *   bit0 is prev->read != 2
+ *   bit1 is next->read != 2
+ */
+#define DEP_RR_BIT (0 + (0 << 1)) /* 0 */
+#define DEP_NR_BIT (1 + (0 << 1)) /* 1 */
+#define DEP_RN_BIT (0 + (1 << 1)) /* 2 */
+#define DEP_NN_BIT (1 + (1 << 1)) /* 3 */
+
+#define DEP_RR_MASK (1U << (DEP_RR_BIT))
+#define DEP_NR_MASK (1U << (DEP_NR_BIT))
+#define DEP_RN_MASK (1U << (DEP_RN_BIT))
+#define DEP_NN_MASK (1U << (DEP_NN_BIT))
+
+static inline unsigned int
+__calc_dep_bit(struct held_lock *prev, struct held_lock *next)
+{
+	return (prev->read != 2) + ((next->read != 2) << 1);
+}
+
+static inline u8 calc_dep(struct held_lock *prev, struct held_lock *next)
+{
+	return 1U << __calc_dep_bit(prev, next);
+}
+
 static enum bfs_result __bfs(struct lock_list *source_entry,
 			     void *data,
 			     int (*match)(struct lock_list *entry, void *data),
@@ -1921,7 +1957,35 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 		if (entry->class == hlock_class(next)) {
 			if (distance == 1)
 				entry->distance = 1;
-			return 1;
+			entry->dep |= calc_dep(prev, next);
+
+			/*
+			 * Also, update the reverse dependency in @next's
+			 * ->locks_before list.
+			 *
+			 *  Here we reuse @entry as the cursor, which is fine
+			 *  because we won't go to the next iteration of the
+			 *  outer loop:
+			 *
+			 *  For normal cases, we return in the inner loop.
+			 *
+			 *  If we fail to return, we have inconsistency, i.e.
+			 *  <prev>::locks_after contains <next> while
+			 *  <next>::locks_before doesn't contain <prev>. In
+			 *  that case, we return after the inner and indicate
+			 *  something is wrong.
+			 */
+			list_for_each_entry(entry, &hlock_class(next)->locks_before, entry) {
+				if (entry->class == hlock_class(prev)) {
+					if (distance == 1)
+						entry->distance = 1;
+					entry->dep |= calc_dep(next, prev);
+					return 1;
+				}
+			}
+
+			/* <prev> is not found in <next>::locks_before */
+			return 0;
 		}
 	}
 
@@ -1948,14 +2012,18 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	 */
 	ret = add_lock_to_list(hlock_class(next),
 			       &hlock_class(prev)->locks_after,
-			       next->acquire_ip, distance, trace);
+			       next->acquire_ip, distance,
+			       calc_dep(prev, next),
+			       trace);
 
 	if (!ret)
 		return 0;
 
 	ret = add_lock_to_list(hlock_class(prev),
 			       &hlock_class(next)->locks_before,
-			       next->acquire_ip, distance, trace);
+			       next->acquire_ip, distance,
+			       calc_dep(next, prev),
+			       trace);
 	if (!ret)
 		return 0;
 
-- 
2.16.2

  parent reply	other threads:[~2018-04-11 13:47 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-11 13:50 [RFC tip/locking/lockdep v6 00/20] lockdep: Support deadlock detection for recursive read locks Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 01/20] lockdep/Documention: Recursive read lock detection reasoning Boqun Feng
2018-04-15  0:38   ` Randy Dunlap
2018-04-16  6:29     ` Boqun Feng
2018-04-27 13:50   ` Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 02/20] lockdep: Demagic the return value of BFS Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 03/20] lockdep: Make __bfs() visit every dependency until a match Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 04/20] lockdep: Redefine LOCK_*_STATE* bits Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 05/20] lockdep: Reduce the size of lock_list::distance Boqun Feng
2018-04-11 13:50 ` Boqun Feng [this message]
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 07/20] lockdep: Extend __bfs() to work with multiple types of dependencies Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 08/20] lockdep: Make __bfs(.match) return bool Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 09/20] lockdep: Support deadlock detection for recursive read locks in check_noncircular() Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 10/20] lockdep: Adjust check_redundant() for recursive read change Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 11/20] lockdep: Fix recursive read lock related safe->unsafe detection Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 12/20] lockdep: Add recursive read locks into dependency graph Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 13/20] lockdep/selftest: Add a R-L/L-W test case specific to chain cache behavior Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 14/20] lockdep: Take read/write status in consideration when generate chainkey Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 15/20] lockdep/selftest: Unleash irq_read_recursion2 and add more Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 16/20] lockdep/selftest: Add more recursive read related test cases Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 17/20] Revert "locking/lockdep/selftests: Fix mixed read-write ABBA tests" Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 18/20] MAINTAINERS: Add myself as a LOCKING PRIMITIVES reviewer Boqun Feng
2018-04-11 13:56 ` [RFC tip/locking/lockdep v6 19/20] rcu: Equip sleepable RCU with lockdep dependency graph checks Boqun Feng
2018-04-11 18:57   ` Paul E. McKenney
2018-04-12  2:12     ` Boqun Feng
2018-04-12  9:12       ` Peter Zijlstra
2018-04-13 13:24         ` Boqun Feng
2018-04-11 13:57 ` [RFC tip/locking/lockdep v6 20/20] lockdep/selftest: Add a test case for SRCU Boqun Feng

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