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authorBoqun Feng <boqun.feng@gmail.com>2020-08-07 15:42:25 +0800
committerPeter Zijlstra <peterz@infradead.org>2020-08-26 12:42:04 +0200
commit3454a36d6a39186de508dd43df590a6363364176 (patch)
treee2cce77c493fabdf9b791e6ce02fe8ad8e8ff96a /kernel/locking
parentbd76eca10de2eb9998d5125b08e8997cbf5508d5 (diff)
lockdep: Introduce lock_list::dep
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: * Exclusive -> Non-recursive dependencies: EN e.g. write_lock(prev) held and try to acquire write_lock(next) or non-recursive read_lock(next), which can be represented as "prev -(EN)-> next" * Shared -> Non-recursive dependencies: SN e.g. read_lock(prev) held and try to acquire write_lock(next) or non-recursive read_lock(next), which can be represented as "prev -(SN)-> next" * Exclusive -> Recursive dependencies: ER e.g. write_lock(prev) held and try to acquire recursive read_lock(next), which can be represented as "prev -(ER)-> next" * Shared -> Recursive dependencies: SR e.g. read_lock(prev) held and try to acquire recursive read_lock(next), which can be represented as "prev -(SR)-> next" So we use 4 bits for the presence of each type in lock_list::dep. Helper functions and macros 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> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200807074238.1632519-7-boqun.feng@gmail.com
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/lockdep.c92
1 files changed, 88 insertions, 4 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 668a983d6405..16ad1b74aa30 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1320,7 +1320,7 @@ static struct lock_list *alloc_list_entry(void)
*/
static int add_lock_to_list(struct lock_class *this,
struct lock_class *links_to, struct list_head *head,
- unsigned long ip, u16 distance,
+ unsigned long ip, u16 distance, u8 dep,
const struct lock_trace *trace)
{
struct lock_list *entry;
@@ -1334,6 +1334,7 @@ static int add_lock_to_list(struct lock_class *this,
entry->class = this;
entry->links_to = links_to;
+ entry->dep = dep;
entry->distance = distance;
entry->trace = trace;
/*
@@ -1499,6 +1500,57 @@ static inline bool bfs_error(enum bfs_result res)
}
/*
+ * DEP_*_BIT in lock_list::dep
+ *
+ * For dependency @prev -> @next:
+ *
+ * SR: @prev is shared reader (->read != 0) and @next is recursive reader
+ * (->read == 2)
+ * ER: @prev is exclusive locker (->read == 0) and @next is recursive reader
+ * SN: @prev is shared reader and @next is non-recursive locker (->read != 2)
+ * EN: @prev is exclusive locker and @next is non-recursive locker
+ *
+ * Note that we define the value of DEP_*_BITs so that:
+ * bit0 is prev->read == 0
+ * bit1 is next->read != 2
+ */
+#define DEP_SR_BIT (0 + (0 << 1)) /* 0 */
+#define DEP_ER_BIT (1 + (0 << 1)) /* 1 */
+#define DEP_SN_BIT (0 + (1 << 1)) /* 2 */
+#define DEP_EN_BIT (1 + (1 << 1)) /* 3 */
+
+#define DEP_SR_MASK (1U << (DEP_SR_BIT))
+#define DEP_ER_MASK (1U << (DEP_ER_BIT))
+#define DEP_SN_MASK (1U << (DEP_SN_BIT))
+#define DEP_EN_MASK (1U << (DEP_EN_BIT))
+
+static inline unsigned int
+__calc_dep_bit(struct held_lock *prev, struct held_lock *next)
+{
+ return (prev->read == 0) + ((next->read != 2) << 1);
+}
+
+static inline u8 calc_dep(struct held_lock *prev, struct held_lock *next)
+{
+ return 1U << __calc_dep_bit(prev, next);
+}
+
+/*
+ * calculate the dep_bit for backwards edges. We care about whether @prev is
+ * shared and whether @next is recursive.
+ */
+static inline unsigned int
+__calc_dep_bitb(struct held_lock *prev, struct held_lock *next)
+{
+ return (next->read != 2) + ((prev->read == 0) << 1);
+}
+
+static inline u8 calc_depb(struct held_lock *prev, struct held_lock *next)
+{
+ return 1U << __calc_dep_bitb(prev, next);
+}
+
+/*
* Forward- or backward-dependency search, used for both circular dependency
* checking and hardirq-unsafe/softirq-unsafe checking.
*/
@@ -2552,7 +2604,35 @@ 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_depb(prev, next);
+ return 1;
+ }
+ }
+
+ /* <prev> is not found in <next>::locks_before */
+ return 0;
}
}
@@ -2579,14 +2659,18 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
*/
ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
&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),
&hlock_class(next)->locks_before,
- next->acquire_ip, distance, *trace);
+ next->acquire_ip, distance,
+ calc_depb(prev, next),
+ *trace);
if (!ret)
return 0;