linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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 03/20] lockdep: Make __bfs() visit every dependency until a match
Date: Wed, 11 Apr 2018 21:50:53 +0800	[thread overview]
Message-ID: <20180411135110.9217-4-boqun.feng@gmail.com> (raw)
In-Reply-To: <20180411135110.9217-1-boqun.feng@gmail.com>

Currently, __bfs() will do a breadth-first search in the dependency
graph and visit each lock class in the graph exactly once, so for
example, in the following graph:

	A ---------> B
	|            ^
	|            |
	+----------> C

a __bfs() call starts at A, will visit B through dependency A -> B and
visit C through dependency A -> C and that's it, IOW, __bfs() will not
visit dependency C -> B.

This is OK for now, as we only have strong dependencies in the
dependency graph, so whenever there is a traverse path from A to B in
__bfs(), it means A has strong dependency to B (IOW, B depends on A
strongly). So no need to visit all dependencies in the graph.

However, as we are going to add recursive-read lock into the dependency
graph, afterwards, not all the paths mean strong dependencies, in the
same example above, dependency A -> B may be a weak dependency and
traverse A -> C -> B may be a strong dependency path. And with the old
way of __bfs() (i.e. visiting every lock class exactly once), we will
miss the strong dependency path, which will result into failing to find
a deadlock. To cure this for the future, we need to find a way for
__bfs() to visit each dependency, rather than each class, exactly once
in the search until we find a match.

The solution is simple:

We used to mark lock_class::lockdep_dependency_gen_id to indicate a
class has been visited in __bfs(), now we change the semantics a little
bit: we now mark lock_class::lockdep_dependency_gen_id to indicate _all
the dependencies_ in its lock_{after,before} have been visited in the
__bfs() (note we only take one direction in a __bfs() search). In this
way, every dependency is guaranteed to be visited until we find a match.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 61 +++++++++++++++++++++++++++---------------------
 1 file changed, 34 insertions(+), 27 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 2dbaff381778..f39a071ef0a8 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -948,24 +948,20 @@ static inline unsigned int  __cq_get_elem_count(struct circular_queue *cq)
 	return (cq->rear - cq->front) & CQ_MASK;
 }
 
-static inline void mark_lock_accessed(struct lock_list *lock,
-					struct lock_list *parent)
+static inline void mark_lock_list_accessed(struct lock_class *class)
 {
-	unsigned long nr;
+	class->dep_gen_id = lockdep_dependency_gen_id;
+}
 
-	nr = lock - list_entries;
-	WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
+static inline void visit_lock_entry(struct lock_list *lock,
+				    struct lock_list *parent)
+{
 	lock->parent = parent;
-	lock->class->dep_gen_id = lockdep_dependency_gen_id;
 }
 
-static inline unsigned long lock_accessed(struct lock_list *lock)
+static inline unsigned long lock_list_accessed(struct lock_class *class)
 {
-	unsigned long nr;
-
-	nr = lock - list_entries;
-	WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
-	return lock->class->dep_gen_id == lockdep_dependency_gen_id;
+	return class->dep_gen_id == lockdep_dependency_gen_id;
 }
 
 static inline struct lock_list *get_lock_parent(struct lock_list *child)
@@ -1054,6 +1050,18 @@ static enum bfs_result __bfs(struct lock_list *source_entry,
 			goto exit;
 		}
 
+		/*
+		 * If we have visited all the dependencies from this @lock to
+		 * others (iow, if we have visited all lock_list entries in
+		 * @lock->class->locks_{after,before}) we skip, otherwise go
+		 * and visit all the dependencies in the list and mark this
+		 * list accessed.
+		 */
+		if (lock_list_accessed(lock->class))
+			continue;
+		else
+			mark_lock_list_accessed(lock->class);
+
 		if (forward)
 			head = &lock->class->locks_after;
 		else
@@ -1062,23 +1070,22 @@ static enum bfs_result __bfs(struct lock_list *source_entry,
 		DEBUG_LOCKS_WARN_ON(!irqs_disabled());
 
 		list_for_each_entry_rcu(entry, head, entry) {
-			if (!lock_accessed(entry)) {
-				unsigned int cq_depth;
-				mark_lock_accessed(entry, lock);
-				if (match(entry, data)) {
-					*target_entry = entry;
-					ret = BFS_RMATCH;
-					goto exit;
-				}
+			unsigned int cq_depth;
 
-				if (__cq_enqueue(cq, (unsigned long)entry)) {
-					ret = BFS_EQUEUEFULL;
-					goto exit;
-				}
-				cq_depth = __cq_get_elem_count(cq);
-				if (max_bfs_queue_depth < cq_depth)
-					max_bfs_queue_depth = cq_depth;
+			visit_lock_entry(entry, lock);
+			if (match(entry, data)) {
+				*target_entry = entry;
+				ret = BFS_RMATCH;
+				goto exit;
+			}
+
+			if (__cq_enqueue(cq, (unsigned long)entry)) {
+				ret = BFS_EQUEUEFULL;
+				goto exit;
 			}
+			cq_depth = __cq_get_elem_count(cq);
+			if (max_bfs_queue_depth < cq_depth)
+				max_bfs_queue_depth = cq_depth;
 		}
 	}
 exit:
-- 
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 ` Boqun Feng [this message]
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 ` [RFC tip/locking/lockdep v6 06/20] lockdep: Introduce lock_list::dep Boqun Feng
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180411135110.9217-4-boqun.feng@gmail.com \
    --to=boqun.feng@gmail.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=parri.andrea@gmail.com \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=peterz@infradead.org \
    --subject='Re: [RFC tip/locking/lockdep v6 03/20] lockdep: Make __bfs() visit every dependency until a match' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).