Hi, I got stuck by btrfs/078 with 1 cpu(2 core) machine. And I notice
this patch maybe the
root cause of it.
commit cb65537ee1134d3cc55c1fa83952bc8eb1212833
Author: David Howells <dhowells@xxxxxxxxxx>
Date: Fri May 10 19:50:26 2013 +0100
Add wait_on_atomic_t() and wake_up_atomic_t()
<snip>
+/*
+ * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
+ * the actions of __wait_on_atomic_t() are permitted return codes. Nonzero
+ * return codes halt waiting and return.
+ */
+static __sched
+int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
+ int (*action)(atomic_t *), unsigned mode)
+{
+ atomic_t *val;
+ int ret = 0;
+
+ do {
+ prepare_to_wait(wq, &q->wait, mode);
+ val = q->key.flags;
+ if (atomic_read(val) == 0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^here,
is this judge ok? if the val not 0,
the most thing we want to do is schedule.
+ ret = (*action)(val);
+ } while (!ret && atomic_read(val) != 0);
+ finish_wait(wq, &q->wait);
+ return ret;
+}
Thanks,
George
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