fs: kill i_alloc_sem
i_alloc_sem is a rather special rw_semaphore. It's the last one that may
be released by a non-owner, and it's write side is always mirrored by
real exclusion. It's intended use it to wait for all pending direct I/O
requests to finish before starting a truncate.
Replace it with a hand-grown construct:
- exclusion for truncates is already guaranteed by i_mutex, so it can
simply fall way
- the reader side is replaced by an i_dio_count member in struct inode
that counts the number of pending direct I/O requests. Truncate can't
proceed as long as it's non-zero
- when i_dio_count reaches non-zero we wake up a pending truncate using
wake_up_bit on a new bit in i_flags
- new references to i_dio_count can't appear while we are waiting for
it to read zero because the direct I/O count always needs i_mutex
(or an equivalent like XFS's i_iolock) for starting a new operation.
This scheme is much simpler, and saves the space of a spinlock_t and a
struct list_head in struct inode (typically 160 bits on a non-debug 64-bit
system).
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index ac97bca..de1d395 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -551,9 +551,8 @@
/*
* ocfs2_dio_end_io is called by the dio core when a dio is finished. We're
- * particularly interested in the aio/dio case. Like the core uses
- * i_alloc_sem, we use the rw_lock DLM lock to protect io on one node from
- * truncation on another.
+ * particularly interested in the aio/dio case. We use the rw_lock DLM lock
+ * to protect io on one node from truncation on another.
*/
static void ocfs2_dio_end_io(struct kiocb *iocb,
loff_t offset,
@@ -569,7 +568,7 @@
BUG_ON(!ocfs2_iocb_is_rw_locked(iocb));
if (ocfs2_iocb_is_sem_locked(iocb)) {
- up_read(&inode->i_alloc_sem);
+ inode_dio_done(inode);
ocfs2_iocb_clear_sem_locked(iocb);
}