xfs: replace i_flock with a sleeping bitlock

We almost never block on i_flock, the exception is synchronous inode
flushing.  Instead of bloating the inode with a 16/24-byte completion
that we abuse as a semaphore just implement it as a bitlock that uses
a bit waitqueue for the rare sleeping path.  This primarily is a
tradeoff between a much smaller inode and a faster non-blocking
path vs faster wakeups, and we are much better off with the former.

A small downside is that we will lose lockdep checking for i_flock, but
given that it's always taken inside the ilock that should be acceptable.

Note that for example the inode writeback locking is implemented in a
very similar way.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 18 insertions, 2 deletions

diff --git a/fs/xfs/xfs_iget.c b/fs/xfs/xfs_iget.c
index f180ce896cd7..a7cf7139f9ad 100644
--- a/fs/xfs/xfs_iget.c
+++ b/fs/xfs/xfs_iget.c
@@ -77,7 +77,7 @@ xfs_inode_alloc(
 
         ASSERT(atomic_read(&ip->i_pincount) == 0);
         ASSERT(!spin_is_locked(&ip->i_flags_lock));
-        ASSERT(completion_done(&ip->i_flush));
+        ASSERT(!xfs_isiflocked(ip));
         ASSERT(ip->i_ino == 0);
 
         mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);
@@ -150,7 +150,7 @@ xfs_inode_free(
         /* asserts to verify all state is correct here */
         ASSERT(atomic_read(&ip->i_pincount) == 0);
         ASSERT(!spin_is_locked(&ip->i_flags_lock));
-        ASSERT(completion_done(&ip->i_flush));
+        ASSERT(!xfs_isiflocked(ip));
 
         /*
          * Because we use RCU freeing we need to ensure the inode always
@@ -713,3 +713,19 @@ xfs_isilocked(
         return 0;
 }
 #endif
+
+void
+__xfs_iflock(
+        struct xfs_inode        *ip)
+{
+        wait_queue_head_t *wq = bit_waitqueue(&ip->i_flags, __XFS_IFLOCK_BIT);
+        DEFINE_WAIT_BIT(wait, &ip->i_flags, __XFS_IFLOCK_BIT);
+
+        do {
+                prepare_to_wait_exclusive(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
+                if (xfs_isiflocked(ip))
+                        io_schedule();
+        } while (!xfs_iflock_nowait(ip));
+
+        finish_wait(wq, &wait.wait);
+}