return err;
}
+/**
+ * __queue_and_wait - queue a task and wait until the task is waked up.
+ * @c: UBIFS file-system description object
+ *
+ * This function adds current task in queue and waits until the task is waked
+ * up. This function should be called with @c->reserve_space_wq locked.
+ */
+static void __queue_and_wait(struct ubifs_info *c)
+{
+ DEFINE_WAIT(wait);
+
+ __add_wait_queue_entry_tail_exclusive(&c->reserve_space_wq, &wait);
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ spin_unlock(&c->reserve_space_wq.lock);
+
+ schedule();
+ finish_wait(&c->reserve_space_wq, &wait);
+}
+
+/**
+ * wait_for_reservation - try queuing current task to wait until waked up.
+ * @c: UBIFS file-system description object
+ *
+ * This function queues current task to wait until waked up, if queuing is
+ * started(@c->need_wait_space is not %0). Returns %true if current task is
+ * added in queue, otherwise %false is returned.
+ */
+static bool wait_for_reservation(struct ubifs_info *c)
+{
+ if (likely(atomic_read(&c->need_wait_space) == 0))
+ /* Quick path to check whether queuing is started. */
+ return false;
+
+ spin_lock(&c->reserve_space_wq.lock);
+ if (atomic_read(&c->need_wait_space) == 0) {
+ /* Queuing is not started, don't queue current task. */
+ spin_unlock(&c->reserve_space_wq.lock);
+ return false;
+ }
+
+ __queue_and_wait(c);
+ return true;
+}
+
+/**
+ * wake_up_reservation - wake up first task in queue or stop queuing.
+ * @c: UBIFS file-system description object
+ *
+ * This function wakes up the first task in queue if it exists, or stops
+ * queuing if no tasks in queue.
+ */
+static void wake_up_reservation(struct ubifs_info *c)
+{
+ spin_lock(&c->reserve_space_wq.lock);
+ if (waitqueue_active(&c->reserve_space_wq))
+ wake_up_locked(&c->reserve_space_wq);
+ else
+ /*
+ * Compared with wait_for_reservation(), set @c->need_wait_space
+ * under the protection of wait queue lock, which can avoid that
+ * @c->need_wait_space is set to 0 after new task queued.
+ */
+ atomic_set(&c->need_wait_space, 0);
+ spin_unlock(&c->reserve_space_wq.lock);
+}
+
+/**
+ * wake_up_reservation - add current task in queue or start queuing.
+ * @c: UBIFS file-system description object
+ *
+ * This function starts queuing if queuing is not started, otherwise adds
+ * current task in queue.
+ */
+static void add_or_start_queue(struct ubifs_info *c)
+{
+ spin_lock(&c->reserve_space_wq.lock);
+ if (atomic_cmpxchg(&c->need_wait_space, 0, 1) == 0) {
+ /* Starts queuing, task can go on directly. */
+ spin_unlock(&c->reserve_space_wq.lock);
+ return;
+ }
+
+ /*
+ * There are at least two tasks have retried more than 32 times
+ * at certain point, first task has started queuing, just queue
+ * the left tasks.
+ */
+ __queue_and_wait(c);
+}
+
/**
* make_reservation - reserve journal space.
* @c: UBIFS file-system description object
static int make_reservation(struct ubifs_info *c, int jhead, int len)
{
int err, cmt_retries = 0, nospc_retries = 0;
+ bool blocked = wait_for_reservation(c);
again:
down_read(&c->commit_sem);
err = reserve_space(c, jhead, len);
- if (!err)
+ if (!err) {
/* c->commit_sem will get released via finish_reservation(). */
- return 0;
+ goto out_wake_up;
+ }
up_read(&c->commit_sem);
if (err == -ENOSPC) {
/*
* GC could not make any progress. We should try to commit
- * once because it could make some dirty space and GC would
- * make progress, so make the error -EAGAIN so that the below
+ * because it could make some dirty space and GC would make
+ * progress, so make the error -EAGAIN so that the below
* will commit and re-try.
*/
- if (nospc_retries++ < 2) {
- dbg_jnl("no space, retry");
- err = -EAGAIN;
- }
-
- /*
- * This means that the budgeting is incorrect. We always have
- * to be able to write to the media, because all operations are
- * budgeted. Deletions are not budgeted, though, but we reserve
- * an extra LEB for them.
- */
+ nospc_retries++;
+ dbg_jnl("no space, retry");
+ err = -EAGAIN;
}
if (err != -EAGAIN)
*/
if (cmt_retries > 128) {
/*
- * This should not happen unless the journal size limitations
- * are too tough.
+ * This should not happen unless:
+ * 1. The journal size limitations are too tough.
+ * 2. The budgeting is incorrect. We always have to be able to
+ * write to the media, because all operations are budgeted.
+ * Deletions are not budgeted, though, but we reserve an
+ * extra LEB for them.
*/
- ubifs_err(c, "stuck in space allocation");
+ ubifs_err(c, "stuck in space allocation, nospc_retries %d",
+ nospc_retries);
err = -ENOSPC;
goto out;
- } else if (cmt_retries > 32)
- ubifs_warn(c, "too many space allocation re-tries (%d)",
- cmt_retries);
+ } else if (cmt_retries > 32) {
+ /*
+ * It's almost impossible to happen, unless there are many tasks
+ * making reservation concurrently and someone task has retried
+ * gc + commit for many times, generated available space during
+ * this period are grabbed by other tasks.
+ * But if it happens, start queuing up all tasks that will make
+ * space reservation, then there is only one task making space
+ * reservation at any time, and it can always make success under
+ * the premise of correct budgeting.
+ */
+ ubifs_warn(c, "too many space allocation cmt_retries (%d) "
+ "nospc_retries (%d), start queuing tasks",
+ cmt_retries, nospc_retries);
+
+ if (!blocked) {
+ blocked = true;
+ add_or_start_queue(c);
+ }
+ }
dbg_jnl("-EAGAIN, commit and retry (retried %d times)",
cmt_retries);
err = ubifs_run_commit(c);
if (err)
- return err;
+ goto out_wake_up;
goto again;
out:
cmt_retries = dbg_check_lprops(c);
up_write(&c->commit_sem);
}
+out_wake_up:
+ if (blocked) {
+ /*
+ * Only tasks that have ever started queuing or ever been queued
+ * can wake up other queued tasks, which can make sure that
+ * there is only one task waked up to make space reservation.
+ * For example:
+ * task A task B task C
+ * make_reservation make_reservation
+ * reserve_space // 0
+ * wake_up_reservation
+ * atomic_cmpxchg // 0, start queuing
+ * reserve_space
+ * wait_for_reservation
+ * __queue_and_wait
+ * add_wait_queue
+ * if (blocked) // false
+ * // So that task C won't be waked up to race with task B
+ */
+ wake_up_reservation(c);
+ }
return err;
}
projects / linux-2.6-microblaze.git / commitdiff