linux-kernel - [RFC 12/60] locking/lockdep: Make cookie generator accessible

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Date:   Fri,  7 Sep 2018 23:39:59 +0200
From:   Jan H. Schönherr <jschoenh@...zon.de>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Jan H. Schönherr <jschoenh@...zon.de>,
        linux-kernel@...r.kernel.org
Subject: [RFC 12/60] locking/lockdep: Make cookie generator accessible

If a dynamic amount of locks needs to be pinned in the same context,
it is impractical to have a cookie per lock. Make the cookie generator
accessible, so that such a group of locks can be (re-)pinned with
just one (shared) cookie.

Signed-off-by: Jan H. Schönherr <jschoenh@...zon.de>
---
 include/linux/lockdep.h  |  2 ++
 kernel/locking/lockdep.c | 21 +++++++++++++++------
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index d93a5ec3077f..06aee3386071 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -363,6 +363,7 @@ struct pin_cookie { unsigned int val; };
 
 #define NIL_COOKIE (struct pin_cookie){ .val = 0U, }
 
+struct pin_cookie lockdep_cookie(void);
 extern struct pin_cookie lock_pin_lock(struct lockdep_map *lock);
 extern void lock_repin_lock(struct lockdep_map *lock, struct pin_cookie);
 extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
@@ -452,6 +453,7 @@ struct pin_cookie { };
 
 #define NIL_COOKIE (struct pin_cookie){ }
 
+#define lockdep_cookie()			(NIL_COOKIE)
 #define lockdep_pin_lock(l)			({ struct pin_cookie cookie; cookie; })
 #define lockdep_repin_lock(l, c)		do { (void)(l); (void)(c); } while (0)
 #define lockdep_unpin_lock(l, c)		do { (void)(l); (void)(c); } while (0)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e406c5fdb41e..76aae27e1736 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3729,6 +3729,20 @@ static int __lock_is_held(const struct lockdep_map *lock, int read)
 	return 0;
 }
 
+struct pin_cookie lockdep_cookie(void)
+{
+	struct pin_cookie cookie;
+
+	/*
+	 * Grab 16bits of randomness; this is sufficient to not
+	 * be guessable and still allows some pin nesting in
+	 * our u32 pin_count.
+	 */
+	cookie.val = 1 + (prandom_u32() >> 16);
+
+	return cookie;
+}
+
 static struct pin_cookie __lock_pin_lock(struct lockdep_map *lock)
 {
 	struct pin_cookie cookie = NIL_COOKIE;
@@ -3742,12 +3756,7 @@ static struct pin_cookie __lock_pin_lock(struct lockdep_map *lock)
 		struct held_lock *hlock = curr->held_locks + i;
 
 		if (match_held_lock(hlock, lock)) {
-			/*
-			 * Grab 16bits of randomness; this is sufficient to not
-			 * be guessable and still allows some pin nesting in
-			 * our u32 pin_count.
-			 */
-			cookie.val = 1 + (prandom_u32() >> 16);
+			cookie = lockdep_cookie();
 			hlock->pin_count += cookie.val;
 			return cookie;
 		}
-- 
2.9.3.1.gcba166c.dirty