io_uring/rw: defer fsnotify calls to task context

In the Linux kernel, the following vulnerability has been resolved:

io_uring/rw: defer fsnotify calls to task context

We can't call these off the kiocb completion as that might be off
soft/hard irq context. Defer the calls to when we process the
task_work for this request. That avoids valid complaints like:

stack backtrace:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.0.0-rc6-syzkaller-00321-g105a36f3694e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_usage_bug kernel/locking/lockdep.c:3961 [inline]
valid_state kernel/locking/lockdep.c:3973 [inline]
mark_lock_irq kernel/locking/lockdep.c:4176 [inline]
mark_lock.part.0.cold+0x18/0xd8 kernel/locking/lockdep.c:4632
mark_lock kernel/locking/lockdep.c:4596 [inline]
mark_usage kernel/locking/lockdep.c:4527 [inline]
__lock_acquire+0x11d9/0x56d0 kernel/locking/lockdep.c:5007
lock_acquire kernel/locking/lockdep.c:5666 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
__fs_reclaim_acquire mm/page_alloc.c:4674 [inline]
fs_reclaim_acquire+0x115/0x160 mm/page_alloc.c:4688
might_alloc include/linux/sched/mm.h:271 [inline]
slab_pre_alloc_hook mm/slab.h:700 [inline]
slab_alloc mm/slab.c:3278 [inline]
__kmem_cache_alloc_lru mm/slab.c:3471 [inline]
kmem_cache_alloc+0x39/0x520 mm/slab.c:3491
fanotify_alloc_fid_event fs/notify/fanotify/fanotify.c:580 [inline]
fanotify_alloc_event fs/notify/fanotify/fanotify.c:813 [inline]
fanotify_handle_event+0x1130/0x3f40 fs/notify/fanotify/fanotify.c:948
send_to_group fs/notify/fsnotify.c:360 [inline]
fsnotify+0xafb/0x1680 fs/notify/fsnotify.c:570
__fsnotify_parent+0x62f/0xa60 fs/notify/fsnotify.c:230
fsnotify_parent include/linux/fsnotify.h:77 [inline]
fsnotify_file include/linux/fsnotify.h:99 [inline]
fsnotify_access include/linux/fsnotify.h:309 [inline]
__io_complete_rw_common+0x485/0x720 io_uring/rw.c:195
io_complete_rw+0x1a/0x1f0 io_uring/rw.c:228
iomap_dio_complete_work fs/iomap/direct-io.c:144 [inline]
iomap_dio_bio_end_io+0x438/0x5e0 fs/iomap/direct-io.c:178
bio_endio+0x5f9/0x780 block/bio.c:1564
req_bio_endio block/blk-mq.c:695 [inline]
blk_update_request+0x3fc/0x1300 block/blk-mq.c:825
scsi_end_request+0x7a/0x9a0 drivers/scsi/scsi_lib.c:541
scsi_io_completion+0x173/0x1f70 drivers/scsi/scsi_lib.c:971
scsi_complete+0x122/0x3b0 drivers/scsi/scsi_lib.c:1438
blk_complete_reqs+0xad/0xe0 block/blk-mq.c:1022
__do_softirq+0x1d3/0x9c6 kernel/softirq.c:571
invoke_softirq kernel/softirq.c:445 [inline]
__irq_exit_rcu+0x123/0x180 kernel/softirq.c:650
irq_exit_rcu+0x5/0x20 kernel/softirq.c:662
common_interrupt+0xa9/0xc0 arch/x86/kernel/irq.c:240