tracing/user_events: Limit max fault-in attempts

When event enablement changes, user_events attempts to update a bit in
the user process. If a fault is hit, an attempt to fault-in the page and
the write is retried if the page made it in. While this normally requires
a couple attempts, it is possible a bad user process could attempt to
cause infinite loops.

Ensure fault-in attempts either sync or async are limited to a max of 10
attempts for each update. When the max is hit, return -EFAULT so another
attempt is not made in all cases.

Link: https://lkml.kernel.org/r/[email protected]

Suggested-by: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Beau Belgrave <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

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