Remove checks for mandatory locks

The Linux VFS handles mandatory locks generically so we shouldn't
need to check for conflicting locks in zfs_read(), zfs_write(), or
zfs_freesp().  Linux 3.18 removed the lock_may_read() and
lock_may_write() interfaces which we were relying on for this
purpose.  Rather than emulating those interfaces we remove the
redundant checks.

Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#2804

module/zfs/zfs_vnops.c

@@ -473,15 +473,6 @@ zfs_read(struct inode *ip, uio_t *uio, int ioflag, cred_t *cr)
 		return (0);
 	}
 
-	/*
-	 * Check for mandatory locks
-	 */
-	if (mandatory_lock(ip) &&
-	    !lock_may_read(ip, uio->uio_loffset, uio->uio_resid)) {
-		ZFS_EXIT(zsb);
-		return (SET_ERROR(EAGAIN));
-	}
-
 	/*
 	 * If we're in FRSYNC mode, sync out this znode before reading it.
 	 */
@@ -650,15 +641,6 @@ zfs_write(struct inode *ip, uio_t *uio, int ioflag, cred_t *cr)
 		return (SET_ERROR(EINVAL));
 	}
 
-	/*
-	 * Check for mandatory locks before calling zfs_range_lock()
-	 * in order to prevent a deadlock with locks set via fcntl().
-	 */
-	if (mandatory_lock(ip) && !lock_may_write(ip, woff, n)) {
-		ZFS_EXIT(zsb);
-		return (SET_ERROR(EAGAIN));
-	}
-
 	/*
 	 * Pre-fault the pages to ensure slow (eg NFS) pages
 	 * don't hold up txg.

module/zfs/zfs_znode.c

@@ -1546,7 +1546,6 @@ zfs_trunc(znode_t *zp, uint64_t end)
 int
 zfs_freesp(znode_t *zp, uint64_t off, uint64_t len, int flag, boolean_t log)
 {
-	struct inode *ip = ZTOI(zp);
 	dmu_tx_t *tx;
 	zfs_sb_t *zsb = ZTOZSB(zp);
 	zilog_t *zilog = zsb->z_log;
@@ -1567,15 +1566,6 @@ zfs_freesp(znode_t *zp, uint64_t off, uint64_t len, int flag, boolean_t log)
 		goto out;
 	}
 
-	/*
-	 * Check for any locks in the region to be freed.
-	 */
-	if (ip->i_flock && mandatory_lock(ip)) {
-		uint64_t length = (len ? len : zp->z_size - off);
-		if (!lock_may_write(ip, off, length))
-			return (SET_ERROR(EAGAIN));
-	}
-
 	if (len == 0) {
 		error = zfs_trunc(zp, off);
 	} else {