xfs: remove "no-allocation" reservations for file creations

If we create a new file we will need an inode, and usually some metadata
in the parent direction.  Aiming for everything to go well despite the
lack of a reservation leads to dirty transactions cancelled under a heavy
create/delete load.  This patch removes those nospace transactions, which
will lead to slightly earlier ENOSPC on some workloads, but instead
prevent file system shutdowns due to cancelling dirty transactions for
others.

A customer could observe assertations failures and shutdowns due to
cancelation of dirty transactions during heavy NFS workloads as shown
below:

2017-05-30 21:17:06 kernel: WARNING: [ 2670.728125] XFS: Assertion failed: error != -ENOSPC, file: fs/xfs/xfs_inode.c, line: 1262

2017-05-30 21:17:06 kernel: WARNING: [ 2670.728222] Call Trace:
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728246]  [<ffffffff81795daf>] dump_stack+0x63/0x81
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728262]  [<ffffffff810a1a5a>] warn_slowpath_common+0x8a/0xc0
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728264]  [<ffffffff810a1b8a>] warn_slowpath_null+0x1a/0x20
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728285]  [<ffffffffa01bf403>] asswarn+0x33/0x40 [xfs]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728308]  [<ffffffffa01bb07e>] xfs_create+0x7be/0x7d0 [xfs]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728329]  [<ffffffffa01b6ffb>] xfs_generic_create+0x1fb/0x2e0 [xfs]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728348]  [<ffffffffa01b7114>] xfs_vn_mknod+0x14/0x20 [xfs]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728366]  [<ffffffffa01b7153>] xfs_vn_create+0x13/0x20 [xfs]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728380]  [<ffffffff81231de5>] vfs_create+0xd5/0x140
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728390]  [<ffffffffa045ddb9>] do_nfsd_create+0x499/0x610 [nfsd]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728396]  [<ffffffffa0465fa5>] nfsd3_proc_create+0x135/0x210 [nfsd]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728401]  [<ffffffffa04561e3>] nfsd_dispatch+0xc3/0x210 [nfsd]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728416]  [<ffffffffa03bfa43>] svc_process_common+0x453/0x6f0 [sunrpc]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728423]  [<ffffffffa03bfdf3>] svc_process+0x113/0x1f0 [sunrpc]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728427]  [<ffffffffa0455bcf>] nfsd+0x10f/0x180 [nfsd]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728432]  [<ffffffffa0455ac0>] ? nfsd_destroy+0x80/0x80 [nfsd]
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728438]  [<ffffffff810c0d58>] kthread+0xd8/0xf0
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728441]  [<ffffffff810c0c80>] ? kthread_create_on_node+0x1b0/0x1b0
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728451]  [<ffffffff8179d962>] ret_from_fork+0x42/0x70
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728453]  [<ffffffff810c0c80>] ? kthread_create_on_node+0x1b0/0x1b0
2017-05-30 21:17:06 kernel: WARNING: [ 2670.728454] ---[ end trace f9822c842fec81d4 ]---

2017-05-30 21:17:06 kernel: ALERT: [ 2670.728477] XFS (sdb): Internal error xfs_trans_cancel at line 983 of file fs/xfs/xfs_trans.c.  Caller xfs_create+0x4ee/0x7d0 [xfs]

2017-05-30 21:17:06 kernel: ALERT: [ 2670.728684] XFS (sdb): Corruption of in-memory data detected. Shutting down filesystem
2017-05-30 21:17:06 kernel: ALERT: [ 2670.728685] XFS (sdb): Please umount the filesystem and rectify the problem(s)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>