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Message-ID: <159851485675.20229.7430053417111193715.tip-bot2@tip-bot2>
Date: Thu, 27 Aug 2020 07:54:16 -0000
From: "tip-bot2 for Boqun Feng" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Boqun Feng <boqun.feng@...il.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/core] lockdep: Take read/write status in consideration
when generate chainkey
The following commit has been merged into the locking/core branch of tip:
Commit-ID: f611e8cf98ec908b9c2c0da6064a660fc6022487
Gitweb: https://git.kernel.org/tip/f611e8cf98ec908b9c2c0da6064a660fc6022487
Author: Boqun Feng <boqun.feng@...il.com>
AuthorDate: Fri, 07 Aug 2020 15:42:33 +08:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 26 Aug 2020 12:42:06 +02:00
lockdep: Take read/write status in consideration when generate chainkey
Currently, the chainkey of a lock chain is a hash sum of the class_idx
of all the held locks, the read/write status are not taken in to
consideration while generating the chainkey. This could result into a
problem, if we have:
P1()
{
read_lock(B);
lock(A);
}
P2()
{
lock(A);
read_lock(B);
}
P3()
{
lock(A);
write_lock(B);
}
, and P1(), P2(), P3() run one by one. And when running P2(), lockdep
detects such a lock chain A -> B is not a deadlock, then it's added in
the chain cache, and then when running P3(), even if it's a deadlock, we
could miss it because of the hit of chain cache. This could be confirmed
by self testcase "chain cached mixed R-L/L-W ".
To resolve this, we use concept "hlock_id" to generate the chainkey, the
hlock_id is a tuple (hlock->class_idx, hlock->read), which fits in a u16
type. With this, the chainkeys are different is the lock sequences have
the same locks but different read/write status.
Besides, since we use "hlock_id" to generate chainkeys, the chain_hlocks
array now store the "hlock_id"s rather than lock_class indexes.
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-15-boqun.feng@gmail.com
---
kernel/locking/lockdep.c | 53 +++++++++++++++++++++++++--------------
1 file changed, 35 insertions(+), 18 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index b87766e..cccf4bc 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -372,6 +372,21 @@ static struct hlist_head classhash_table[CLASSHASH_SIZE];
static struct hlist_head chainhash_table[CHAINHASH_SIZE];
/*
+ * the id of held_lock
+ */
+static inline u16 hlock_id(struct held_lock *hlock)
+{
+ BUILD_BUG_ON(MAX_LOCKDEP_KEYS_BITS + 2 > 16);
+
+ return (hlock->class_idx | (hlock->read << MAX_LOCKDEP_KEYS_BITS));
+}
+
+static inline unsigned int chain_hlock_class_idx(u16 hlock_id)
+{
+ return hlock_id & (MAX_LOCKDEP_KEYS - 1);
+}
+
+/*
* The hash key of the lock dependency chains is a hash itself too:
* it's a hash of all locks taken up to that lock, including that lock.
* It's a 64-bit hash, because it's important for the keys to be
@@ -3202,7 +3217,10 @@ static inline void free_chain_hlocks(int base, int size)
struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
{
- return lock_classes + chain_hlocks[chain->base + i];
+ u16 chain_hlock = chain_hlocks[chain->base + i];
+ unsigned int class_idx = chain_hlock_class_idx(chain_hlock);
+
+ return lock_classes + class_idx - 1;
}
/*
@@ -3228,12 +3246,12 @@ static inline int get_first_held_lock(struct task_struct *curr,
/*
* Returns the next chain_key iteration
*/
-static u64 print_chain_key_iteration(int class_idx, u64 chain_key)
+static u64 print_chain_key_iteration(u16 hlock_id, u64 chain_key)
{
- u64 new_chain_key = iterate_chain_key(chain_key, class_idx);
+ u64 new_chain_key = iterate_chain_key(chain_key, hlock_id);
- printk(" class_idx:%d -> chain_key:%016Lx",
- class_idx,
+ printk(" hlock_id:%d -> chain_key:%016Lx",
+ (unsigned int)hlock_id,
(unsigned long long)new_chain_key);
return new_chain_key;
}
@@ -3250,12 +3268,12 @@ print_chain_keys_held_locks(struct task_struct *curr, struct held_lock *hlock_ne
hlock_next->irq_context);
for (; i < depth; i++) {
hlock = curr->held_locks + i;
- chain_key = print_chain_key_iteration(hlock->class_idx, chain_key);
+ chain_key = print_chain_key_iteration(hlock_id(hlock), chain_key);
print_lock(hlock);
}
- print_chain_key_iteration(hlock_next->class_idx, chain_key);
+ print_chain_key_iteration(hlock_id(hlock_next), chain_key);
print_lock(hlock_next);
}
@@ -3263,14 +3281,14 @@ static void print_chain_keys_chain(struct lock_chain *chain)
{
int i;
u64 chain_key = INITIAL_CHAIN_KEY;
- int class_id;
+ u16 hlock_id;
printk("depth: %u\n", chain->depth);
for (i = 0; i < chain->depth; i++) {
- class_id = chain_hlocks[chain->base + i];
- chain_key = print_chain_key_iteration(class_id, chain_key);
+ hlock_id = chain_hlocks[chain->base + i];
+ chain_key = print_chain_key_iteration(hlock_id, chain_key);
- print_lock_name(lock_classes + class_id);
+ print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id) - 1);
printk("\n");
}
}
@@ -3319,7 +3337,7 @@ static int check_no_collision(struct task_struct *curr,
}
for (j = 0; j < chain->depth - 1; j++, i++) {
- id = curr->held_locks[i].class_idx;
+ id = hlock_id(&curr->held_locks[i]);
if (DEBUG_LOCKS_WARN_ON(chain_hlocks[chain->base + j] != id)) {
print_collision(curr, hlock, chain);
@@ -3368,7 +3386,6 @@ static inline int add_chain_cache(struct task_struct *curr,
struct held_lock *hlock,
u64 chain_key)
{
- struct lock_class *class = hlock_class(hlock);
struct hlist_head *hash_head = chainhashentry(chain_key);
struct lock_chain *chain;
int i, j;
@@ -3411,11 +3428,11 @@ static inline int add_chain_cache(struct task_struct *curr,
chain->base = j;
for (j = 0; j < chain->depth - 1; j++, i++) {
- int lock_id = curr->held_locks[i].class_idx;
+ int lock_id = hlock_id(curr->held_locks + i);
chain_hlocks[chain->base + j] = lock_id;
}
- chain_hlocks[chain->base + j] = class - lock_classes;
+ chain_hlocks[chain->base + j] = hlock_id(hlock);
hlist_add_head_rcu(&chain->entry, hash_head);
debug_atomic_inc(chain_lookup_misses);
inc_chains(chain->irq_context);
@@ -3602,7 +3619,7 @@ static void check_chain_key(struct task_struct *curr)
if (prev_hlock && (prev_hlock->irq_context !=
hlock->irq_context))
chain_key = INITIAL_CHAIN_KEY;
- chain_key = iterate_chain_key(chain_key, hlock->class_idx);
+ chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
prev_hlock = hlock;
}
if (chain_key != curr->curr_chain_key) {
@@ -4749,7 +4766,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
chain_key = INITIAL_CHAIN_KEY;
chain_head = 1;
}
- chain_key = iterate_chain_key(chain_key, class_idx);
+ chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
if (nest_lock && !__lock_is_held(nest_lock, -1)) {
print_lock_nested_lock_not_held(curr, hlock, ip);
@@ -5648,7 +5665,7 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
int i;
for (i = chain->base; i < chain->base + chain->depth; i++) {
- if (chain_hlocks[i] != class - lock_classes)
+ if (chain_hlock_class_idx(chain_hlocks[i]) != class - lock_classes)
continue;
/*
* Each lock class occurs at most once in a lock chain so once
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