Update Linux to v5.10.109
Sourced from [1]
[1] https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.10.109.tar.xz
Change-Id: I19bca9fc6762d4e63bcf3e4cba88bbe560d9c76c
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 364d38a..70a32a5 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -1,27 +1,29 @@
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/atomic.h>
-#include <linux/rwsem.h>
#include <linux/percpu.h>
+#include <linux/wait.h>
#include <linux/lockdep.h>
#include <linux/percpu-rwsem.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
+#include <linux/sched/task.h>
#include <linux/errno.h>
-#include "rwsem.h"
-
int __percpu_init_rwsem(struct percpu_rw_semaphore *sem,
- const char *name, struct lock_class_key *rwsem_key)
+ const char *name, struct lock_class_key *key)
{
sem->read_count = alloc_percpu(int);
if (unlikely(!sem->read_count))
return -ENOMEM;
- /* ->rw_sem represents the whole percpu_rw_semaphore for lockdep */
rcu_sync_init(&sem->rss);
- __init_rwsem(&sem->rw_sem, name, rwsem_key);
rcuwait_init(&sem->writer);
- sem->readers_block = 0;
+ init_waitqueue_head(&sem->waiters);
+ atomic_set(&sem->block, 0);
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ debug_check_no_locks_freed((void *)sem, sizeof(*sem));
+ lockdep_init_map(&sem->dep_map, name, key, 0);
+#endif
return 0;
}
EXPORT_SYMBOL_GPL(__percpu_init_rwsem);
@@ -41,74 +43,141 @@
}
EXPORT_SYMBOL_GPL(percpu_free_rwsem);
-int __percpu_down_read(struct percpu_rw_semaphore *sem, int try)
+static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
{
+ this_cpu_inc(*sem->read_count);
+
/*
* Due to having preemption disabled the decrement happens on
* the same CPU as the increment, avoiding the
* increment-on-one-CPU-and-decrement-on-another problem.
*
- * If the reader misses the writer's assignment of readers_block, then
- * the writer is guaranteed to see the reader's increment.
+ * If the reader misses the writer's assignment of sem->block, then the
+ * writer is guaranteed to see the reader's increment.
*
* Conversely, any readers that increment their sem->read_count after
- * the writer looks are guaranteed to see the readers_block value,
- * which in turn means that they are guaranteed to immediately
- * decrement their sem->read_count, so that it doesn't matter that the
- * writer missed them.
+ * the writer looks are guaranteed to see the sem->block value, which
+ * in turn means that they are guaranteed to immediately decrement
+ * their sem->read_count, so that it doesn't matter that the writer
+ * missed them.
*/
smp_mb(); /* A matches D */
/*
- * If !readers_block the critical section starts here, matched by the
+ * If !sem->block the critical section starts here, matched by the
* release in percpu_up_write().
*/
- if (likely(!smp_load_acquire(&sem->readers_block)))
+ if (likely(!atomic_read_acquire(&sem->block)))
+ return true;
+
+ this_cpu_dec(*sem->read_count);
+
+ /* Prod writer to re-evaluate readers_active_check() */
+ rcuwait_wake_up(&sem->writer);
+
+ return false;
+}
+
+static inline bool __percpu_down_write_trylock(struct percpu_rw_semaphore *sem)
+{
+ if (atomic_read(&sem->block))
+ return false;
+
+ return atomic_xchg(&sem->block, 1) == 0;
+}
+
+static bool __percpu_rwsem_trylock(struct percpu_rw_semaphore *sem, bool reader)
+{
+ if (reader) {
+ bool ret;
+
+ preempt_disable();
+ ret = __percpu_down_read_trylock(sem);
+ preempt_enable();
+
+ return ret;
+ }
+ return __percpu_down_write_trylock(sem);
+}
+
+/*
+ * The return value of wait_queue_entry::func means:
+ *
+ * <0 - error, wakeup is terminated and the error is returned
+ * 0 - no wakeup, a next waiter is tried
+ * >0 - woken, if EXCLUSIVE, counted towards @nr_exclusive.
+ *
+ * We use EXCLUSIVE for both readers and writers to preserve FIFO order,
+ * and play games with the return value to allow waking multiple readers.
+ *
+ * Specifically, we wake readers until we've woken a single writer, or until a
+ * trylock fails.
+ */
+static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry,
+ unsigned int mode, int wake_flags,
+ void *key)
+{
+ bool reader = wq_entry->flags & WQ_FLAG_CUSTOM;
+ struct percpu_rw_semaphore *sem = key;
+ struct task_struct *p;
+
+ /* concurrent against percpu_down_write(), can get stolen */
+ if (!__percpu_rwsem_trylock(sem, reader))
return 1;
+ p = get_task_struct(wq_entry->private);
+ list_del_init(&wq_entry->entry);
+ smp_store_release(&wq_entry->private, NULL);
+
+ wake_up_process(p);
+ put_task_struct(p);
+
+ return !reader; /* wake (readers until) 1 writer */
+}
+
+static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
+{
+ DEFINE_WAIT_FUNC(wq_entry, percpu_rwsem_wake_function);
+ bool wait;
+
+ spin_lock_irq(&sem->waiters.lock);
/*
- * Per the above comment; we still have preemption disabled and
- * will thus decrement on the same CPU as we incremented.
+ * Serialize against the wakeup in percpu_up_write(), if we fail
+ * the trylock, the wakeup must see us on the list.
*/
- __percpu_up_read(sem);
+ wait = !__percpu_rwsem_trylock(sem, reader);
+ if (wait) {
+ wq_entry.flags |= WQ_FLAG_EXCLUSIVE | reader * WQ_FLAG_CUSTOM;
+ __add_wait_queue_entry_tail(&sem->waiters, &wq_entry);
+ }
+ spin_unlock_irq(&sem->waiters.lock);
+
+ while (wait) {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ if (!smp_load_acquire(&wq_entry.private))
+ break;
+ schedule();
+ }
+ __set_current_state(TASK_RUNNING);
+}
+
+bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
+{
+ if (__percpu_down_read_trylock(sem))
+ return true;
if (try)
- return 0;
+ return false;
- /*
- * We either call schedule() in the wait, or we'll fall through
- * and reschedule on the preempt_enable() in percpu_down_read().
- */
- preempt_enable_no_resched();
-
- /*
- * Avoid lockdep for the down/up_read() we already have them.
- */
- __down_read(&sem->rw_sem);
- this_cpu_inc(*sem->read_count);
- __up_read(&sem->rw_sem);
-
+ preempt_enable();
+ percpu_rwsem_wait(sem, /* .reader = */ true);
preempt_disable();
- return 1;
+
+ return true;
}
EXPORT_SYMBOL_GPL(__percpu_down_read);
-void __percpu_up_read(struct percpu_rw_semaphore *sem)
-{
- smp_mb(); /* B matches C */
- /*
- * In other words, if they see our decrement (presumably to aggregate
- * zero, as that is the only time it matters) they will also see our
- * critical section.
- */
- __this_cpu_dec(*sem->read_count);
-
- /* Prod writer to recheck readers_active */
- rcuwait_wake_up(&sem->writer);
-}
-EXPORT_SYMBOL_GPL(__percpu_up_read);
-
#define per_cpu_sum(var) \
({ \
typeof(var) __sum = 0; \
@@ -124,6 +193,8 @@
* zero. If this sum is zero, then it is stable due to the fact that if any
* newly arriving readers increment a given counter, they will immediately
* decrement that same counter.
+ *
+ * Assumes sem->block is set.
*/
static bool readers_active_check(struct percpu_rw_semaphore *sem)
{
@@ -142,32 +213,36 @@
void percpu_down_write(struct percpu_rw_semaphore *sem)
{
+ might_sleep();
+ rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
+
/* Notify readers to take the slow path. */
rcu_sync_enter(&sem->rss);
- down_write(&sem->rw_sem);
+ /*
+ * Try set sem->block; this provides writer-writer exclusion.
+ * Having sem->block set makes new readers block.
+ */
+ if (!__percpu_down_write_trylock(sem))
+ percpu_rwsem_wait(sem, /* .reader = */ false);
+
+ /* smp_mb() implied by __percpu_down_write_trylock() on success -- D matches A */
/*
- * Notify new readers to block; up until now, and thus throughout the
- * longish rcu_sync_enter() above, new readers could still come in.
- */
- WRITE_ONCE(sem->readers_block, 1);
-
- smp_mb(); /* D matches A */
-
- /*
- * If they don't see our writer of readers_block, then we are
- * guaranteed to see their sem->read_count increment, and therefore
- * will wait for them.
+ * If they don't see our store of sem->block, then we are guaranteed to
+ * see their sem->read_count increment, and therefore will wait for
+ * them.
*/
- /* Wait for all now active readers to complete. */
- rcuwait_wait_event(&sem->writer, readers_active_check(sem));
+ /* Wait for all active readers to complete. */
+ rcuwait_wait_event(&sem->writer, readers_active_check(sem), TASK_UNINTERRUPTIBLE);
}
EXPORT_SYMBOL_GPL(percpu_down_write);
void percpu_up_write(struct percpu_rw_semaphore *sem)
{
+ rwsem_release(&sem->dep_map, _RET_IP_);
+
/*
* Signal the writer is done, no fast path yet.
*
@@ -178,12 +253,12 @@
* Therefore we force it through the slow path which guarantees an
* acquire and thereby guarantees the critical section's consistency.
*/
- smp_store_release(&sem->readers_block, 0);
+ atomic_set_release(&sem->block, 0);
/*
- * Release the write lock, this will allow readers back in the game.
+ * Prod any pending reader/writer to make progress.
*/
- up_write(&sem->rw_sem);
+ __wake_up(&sem->waiters, TASK_NORMAL, 1, sem);
/*
* Once this completes (at least one RCU-sched grace period hence) the