btrfs: add a i_mmap_lock to our inode

We need to be able to exclude page_mkwrite from happening concurrently
with certain operations.  To facilitate this, add a i_mmap_lock to our
inode, down_read() it in our mkwrite, and add a new ILOCK flag to
indicate that we want to take the i_mmap_lock as well.  I used pahole to
check the size of the btrfs_inode, the sizes are as follows

no lockdep:
before: 1120 (3 per 4k page)
after: 1160 (3 per 4k page)

lockdep:
before: 2072 (1 per 4k page)
after: 2224 (1 per 4k page)

We're slightly larger but it doesn't change how many objects we can fit
per page.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 5776026c532e..751ab9f80e4c 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3178,6 +3178,7 @@ extern const struct iomap_dio_ops btrfs_dio_ops;
 /* Inode locking type flags, by default the exclusive lock is taken */
 #define BTRFS_ILOCK_SHARED	(1U << 0)
 #define BTRFS_ILOCK_TRY 	(1U << 1)
+#define BTRFS_ILOCK_MMAP	(1U << 2)
 
 int btrfs_inode_lock(struct inode *inode, unsigned int ilock_flags);
 void btrfs_inode_unlock(struct inode *inode, unsigned int ilock_flags);