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authorLinus Torvalds <torvalds@linux-foundation.org>2020-09-20 15:25:33 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-09-20 15:25:33 -0700
commit3d491679b880006d2469ad14f73c2debb2a522bd (patch)
treec28cc001fea96b7cbaf993ed89bd639d28eca3ea
parent5674d81c21d47e12c2def2df7360ef2dbca108e6 (diff)
parente6b1a44eccfcab5e5e280be376f65478c3b2c7a2 (diff)
Merge tag 'locking_urgent_for_v5.9_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixes from Borislav Petkov: "Two fixes from the locking/urgent pile: - Fix lockdep's detection of "USED" <- "IN-NMI" inversions (Peter Zijlstra) - Make percpu-rwsem operations on the semaphore's ->read_count IRQ-safe because it can be used in an IRQ context (Hou Tao)" * tag 'locking_urgent_for_v5.9_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: locking/percpu-rwsem: Use this_cpu_{inc,dec}() for read_count locking/lockdep: Fix "USED" <- "IN-NMI" inversions
-rw-r--r--include/linux/percpu-rwsem.h8
-rw-r--r--kernel/locking/lockdep.c35
-rw-r--r--kernel/locking/lockdep_internals.h2
-rw-r--r--kernel/locking/percpu-rwsem.c4
4 files changed, 37 insertions, 12 deletions
diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index 5e033fe1ff4e..5fda40f97fe9 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -60,7 +60,7 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
* anything we did within this RCU-sched read-size critical section.
*/
if (likely(rcu_sync_is_idle(&sem->rss)))
- __this_cpu_inc(*sem->read_count);
+ this_cpu_inc(*sem->read_count);
else
__percpu_down_read(sem, false); /* Unconditional memory barrier */
/*
@@ -79,7 +79,7 @@ static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
* Same as in percpu_down_read().
*/
if (likely(rcu_sync_is_idle(&sem->rss)))
- __this_cpu_inc(*sem->read_count);
+ this_cpu_inc(*sem->read_count);
else
ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
preempt_enable();
@@ -103,7 +103,7 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
* Same as in percpu_down_read().
*/
if (likely(rcu_sync_is_idle(&sem->rss))) {
- __this_cpu_dec(*sem->read_count);
+ this_cpu_dec(*sem->read_count);
} else {
/*
* slowpath; reader will only ever wake a single blocked
@@ -115,7 +115,7 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
* aggregate zero, as that is the only time it matters) they
* will also see our critical section.
*/
- __this_cpu_dec(*sem->read_count);
+ this_cpu_dec(*sem->read_count);
rcuwait_wake_up(&sem->writer);
}
preempt_enable();
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 54b74fabf40c..2facbbd146ec 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3969,13 +3969,18 @@ static int separate_irq_context(struct task_struct *curr,
static int mark_lock(struct task_struct *curr, struct held_lock *this,
enum lock_usage_bit new_bit)
{
- unsigned int new_mask = 1 << new_bit, ret = 1;
+ unsigned int old_mask, new_mask, ret = 1;
if (new_bit >= LOCK_USAGE_STATES) {
DEBUG_LOCKS_WARN_ON(1);
return 0;
}
+ if (new_bit == LOCK_USED && this->read)
+ new_bit = LOCK_USED_READ;
+
+ new_mask = 1 << new_bit;
+
/*
* If already set then do not dirty the cacheline,
* nor do any checks:
@@ -3988,13 +3993,22 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
/*
* Make sure we didn't race:
*/
- if (unlikely(hlock_class(this)->usage_mask & new_mask)) {
- graph_unlock();
- return 1;
- }
+ if (unlikely(hlock_class(this)->usage_mask & new_mask))
+ goto unlock;
+ old_mask = hlock_class(this)->usage_mask;
hlock_class(this)->usage_mask |= new_mask;
+ /*
+ * Save one usage_traces[] entry and map both LOCK_USED and
+ * LOCK_USED_READ onto the same entry.
+ */
+ if (new_bit == LOCK_USED || new_bit == LOCK_USED_READ) {
+ if (old_mask & (LOCKF_USED | LOCKF_USED_READ))
+ goto unlock;
+ new_bit = LOCK_USED;
+ }
+
if (!(hlock_class(this)->usage_traces[new_bit] = save_trace()))
return 0;
@@ -4008,6 +4022,7 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
return 0;
}
+unlock:
graph_unlock();
/*
@@ -4942,12 +4957,20 @@ static void verify_lock_unused(struct lockdep_map *lock, struct held_lock *hlock
{
#ifdef CONFIG_PROVE_LOCKING
struct lock_class *class = look_up_lock_class(lock, subclass);
+ unsigned long mask = LOCKF_USED;
/* if it doesn't have a class (yet), it certainly hasn't been used yet */
if (!class)
return;
- if (!(class->usage_mask & LOCK_USED))
+ /*
+ * READ locks only conflict with USED, such that if we only ever use
+ * READ locks, there is no deadlock possible -- RCU.
+ */
+ if (!hlock->read)
+ mask |= LOCKF_USED_READ;
+
+ if (!(class->usage_mask & mask))
return;
hlock->class_idx = class - lock_classes;
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index baca699b94e9..b0be1560ed17 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -19,6 +19,7 @@ enum lock_usage_bit {
#include "lockdep_states.h"
#undef LOCKDEP_STATE
LOCK_USED,
+ LOCK_USED_READ,
LOCK_USAGE_STATES
};
@@ -40,6 +41,7 @@ enum {
#include "lockdep_states.h"
#undef LOCKDEP_STATE
__LOCKF(USED)
+ __LOCKF(USED_READ)
};
#define LOCKDEP_STATE(__STATE) LOCKF_ENABLED_##__STATE |
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 8bbafe3e5203..70a32a576f3f 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -45,7 +45,7 @@ EXPORT_SYMBOL_GPL(percpu_free_rwsem);
static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
{
- __this_cpu_inc(*sem->read_count);
+ this_cpu_inc(*sem->read_count);
/*
* Due to having preemption disabled the decrement happens on
@@ -71,7 +71,7 @@ static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
if (likely(!atomic_read_acquire(&sem->block)))
return true;
- __this_cpu_dec(*sem->read_count);
+ this_cpu_dec(*sem->read_count);
/* Prod writer to re-evaluate readers_active_check() */
rcuwait_wake_up(&sem->writer);