NFSD: Add an nfsd_file_fsync tracepoint

[ Upstream commit d7064eaf

 ]

Add a tracepoint to capture the number of filecache-triggered fsync
calls and which files needed it. Also, record when an fsync triggers
a write verifier reset.

Examples:

<...>-97    [007]   262.505611: nfsd_file_free:       inode=0xffff888171e08140 ref=0 flags=GC may=WRITE nf_file=0xffff8881373d2400
<...>-97    [007]   262.505612: nfsd_file_fsync:      inode=0xffff888171e08140 ref=0 flags=GC may=WRITE nf_file=0xffff8881373d2400 ret=0
<...>-97    [007]   262.505623: nfsd_file_free:       inode=0xffff888171e08dc0 ref=0 flags=GC may=WRITE nf_file=0xffff8881373d1e00
<...>-97    [007]   262.505624: nfsd_file_fsync:      inode=0xffff888171e08dc0 ref=0 flags=GC may=WRITE nf_file=0xffff8881373d1e00 ret=0

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Stable-dep-of: 0b3a551f

 ("nfsd: fix handling of cached open files in nfsd4_open codepath")
Signed-off-by: Sasha Levin <sashal@kernel.org>