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/reiserfs/xattr.c b/fs/reiserfs/xattr.c
index 4ea2ab4..6938d8c 100644
--- a/fs/reiserfs/xattr.c
+++ b/fs/reiserfs/xattr.c
@@ -555,11 +555,10 @@
reiserfs_write_unlock(inode->i_sb);
mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_XATTR);
- down_write(&dentry->d_inode->i_alloc_sem);
+ inode_dio_wait(dentry->d_inode);
reiserfs_write_lock(inode->i_sb);
err = reiserfs_setattr(dentry, &newattrs);
- up_write(&dentry->d_inode->i_alloc_sem);
mutex_unlock(&dentry->d_inode->i_mutex);
} else
update_ctime(inode);