tracing: Fix overflow in get_free_elt()

"tracing_map->next_elt" in get_free_elt() is at risk of overflowing.

Once it overflows, new elements can still be inserted into the tracing_map
even though the maximum number of elements (`max_elts`) has been reached.
Continuing to insert elements after the overflow could result in the
tracing_map containing "tracing_map->max_size" elements, leaving no empty
entries.
If any attempt is made to insert an element into a full tracing_map using
`__tracing_map_insert()`, it will cause an infinite loop with preemption
disabled, leading to a CPU hang problem.

Fix this by preventing any further increments to "tracing_map->next_elt"
once it reaches "tracing_map->max_elt".

Cc: [email protected]
Cc: Masami Hiramatsu <[email protected]>
Fixes: 08d43a5fa063e ("tracing: Add lock-free tracing_map")
Co-developed-by: Cheng-Jui Wang <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Cheng-Jui Wang <[email protected]>
Signed-off-by: Tze-nan Wu <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

0 files changed, 0 insertions, 0 deletions