tracing: Verify target file before registering a uprobe event

tracing: Verify target file before registering a uprobe event

Without this patch, we can register a uprobe event for a directory.
Enabling such a uprobe event would anyway fail.

Example:
$ echo 'p /bin:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events

However dirctories cannot be valid targets for uprobe.
Hence verify if the target is a regular file during the probe
registration.

Link: http://lkml.kernel.org/r/[email protected]
Cc: Namhyung Kim <[email protected]>
Signed-off-by: Jovi Zhang <[email protected]>
Acked-by: Srikar Dronamraju <[email protected]>
[ cleaned up whitespace and removed redundant IS_DIR() check ]
Signed-off-by: Steven Rostedt <[email protected]>