xfs_trans_add_item() is called with ip->i_ilock held, which means it
is unsafe for memory reclaim to recurse back into the filesystem
(ilock is required in writeback). Hence the allocation needs to be
KM_NOFS to avoid recursion.

Lockdep report indicating memory allocation being called with the
ip->i_ilock held is as follows:

[ 1749.866796] =================================
[ 1749.867788] [ INFO: inconsistent lock state ]
[ 1749.868327] 2.6.35-rc3-dgc+ #25
[ 1749.868741] ---------------------------------
[ 1749.868741] inconsistent {IN-RECLAIM_FS-W} -> {RECLAIM_FS-ON-W} usage.
[ 1749.868741] dd/2835 [HC0[0]:SC0[0]:HE1:SE1] takes:
[ 1749.868741]  (&(&ip->i_lock)->mr_lock){++++?.}, at: [<ffffffff813170fb>] xfs_ilock+0x10b/0x190
[ 1749.868741] {IN-RECLAIM_FS-W} state was registered at:
[ 1749.868741]   [<ffffffff810b3a97>] __lock_acquire+0x437/0x1450
[ 1749.868741]   [<ffffffff810b4b56>] lock_acquire+0xa6/0x160
[ 1749.868741]   [<ffffffff810a20b5>] down_write_nested+0x65/0xb0
[ 1749.868741]   [<ffffffff813170fb>] xfs_ilock+0x10b/0x190
[ 1749.868741]   [<ffffffff8134e819>] xfs_reclaim_inode+0x99/0x310
[ 1749.868741]   [<ffffffff8134f56b>] xfs_inode_ag_walk+0x8b/0x150
[ 1749.868741]   [<ffffffff8134f6bb>] xfs_inode_ag_iterator+0x8b/0xf0
[ 1749.868741]   [<ffffffff8134f7a8>] xfs_reclaim_inode_shrink+0x88/0x90
[ 1749.868741]   [<ffffffff81119d07>] shrink_slab+0x137/0x1a0
[ 1749.868741]   [<ffffffff8111bbe1>] balance_pgdat+0x421/0x6a0
[ 1749.868741]   [<ffffffff8111bf7d>] kswapd+0x11d/0x320
[ 1749.868741]   [<ffffffff8109ce56>] kthread+0x96/0xa0
[ 1749.868741]   [<ffffffff81035de4>] kernel_thread_helper+0x4/0x10
[ 1749.868741] irq event stamp: 4234335
[ 1749.868741] hardirqs last  enabled at (4234335): [<ffffffff81147d25>] kmem_cache_free+0x115/0x220
[ 1749.868741] hardirqs last disabled at (4234334): [<ffffffff81147c4d>] kmem_cache_free+0x3d/0x220
[ 1749.868741] softirqs last  enabled at (4233112): [<ffffffff81084dd2>] __do_softirq+0x142/0x260
[ 1749.868741] softirqs last disabled at (4233095): [<ffffffff81035edc>] call_softirq+0x1c/0x50
[ 1749.868741] 
[ 1749.868741] other info that might help us debug this:
[ 1749.868741] 2 locks held by dd/2835:
[ 1749.868741]  #0:  (&(&ip->i_iolock)->mr_lock#2){+.+.+.}, at: [<ffffffff81316edd>] xfs_ilock_nowait+0xed/0x200
[ 1749.868741]  #1:  (&(&ip->i_lock)->mr_lock){++++?.}, at: [<ffffffff813170fb>] xfs_ilock+0x10b/0x190
[ 1749.868741] 
[ 1749.868741] stack backtrace:
[ 1749.868741] Pid: 2835, comm: dd Not tainted 2.6.35-rc3-dgc+ #25
[ 1749.868741] Call Trace:
[ 1749.868741]  [<ffffffff810b1faa>] print_usage_bug+0x18a/0x190
[ 1749.868741]  [<ffffffff8104264f>] ? save_stack_trace+0x2f/0x50
[ 1749.868741]  [<ffffffff810b2400>] ? check_usage_backwards+0x0/0xf0
[ 1749.868741]  [<ffffffff810b2f11>] mark_lock+0x331/0x400
[ 1749.868741]  [<ffffffff810b3047>] mark_held_locks+0x67/0x90
[ 1749.868741]  [<ffffffff810b3111>] lockdep_trace_alloc+0xa1/0xe0
[ 1749.868741]  [<ffffffff81147419>] kmem_cache_alloc+0x39/0x1e0
[ 1749.868741]  [<ffffffff8133f954>] kmem_zone_alloc+0x94/0xe0
[ 1749.868741]  [<ffffffff8133f9be>] kmem_zone_zalloc+0x1e/0x50
[ 1749.868741]  [<ffffffff81335f02>] xfs_trans_add_item+0x72/0xb0
[ 1749.868741]  [<ffffffff81339e41>] xfs_trans_ijoin+0xa1/0xd0
[ 1749.868741]  [<ffffffff81319f82>] xfs_itruncate_finish+0x312/0x5d0
[ 1749.868741]  [<ffffffff8133cb87>] xfs_free_eofblocks+0x227/0x280
[ 1749.868741]  [<ffffffff8133cd18>] xfs_release+0x138/0x190
[ 1749.868741]  [<ffffffff813464c5>] xfs_file_release+0x15/0x20
[ 1749.868741]  [<ffffffff81150ebf>] fput+0x13f/0x260
[ 1749.868741]  [<ffffffff8114d8c2>] filp_close+0x52/0x80
[ 1749.868741]  [<ffffffff8114d9a9>] sys_close+0xb9/0x120
[ 1749.868741]  [<ffffffff81034ff2>] system_call_fastpath+0x16/0x1b

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>