Hi,

Fifth batch of pre-existing bugs found by sashiko-bot during AI-assisted
review of the perf-data-validation hardening series.  All are independent
of that series -- they are latent bugs in surrounding code exposed during
review.

  1. perf_mmap__aio_mmap() sets nr_cblocks before allocating arrays.
     If calloc() fails, cleanup dereferences NULL map->aio.data.

  2. env->cpu can be NULL when reading old-format perf.data that
     predates topology info (process_cpu_topology() frees it while
     nr_cpus_avail remains set).  The six topology aggregation
     callbacks in builtin-stat.c dereference NULL.  Introduces
     perf_env__get_cpu_topology() accessor with the NULL/bounds guard.

  3. he__get_c2c_hists() error path frees hists without clearing
     c2c_he->hists.  Teardown finds the dangling pointer and calls
     hists__delete_entries() on freed memory.

  4. cpu2y() indexes topology_map[] without bounds check.  Also fixes
     str_to_bitmap() where perf_cpu_map__new("") returns cpu.cpu == -1,
     bypassing the signed >= nr_cpus check and calling __set_bit(-1, ...).

  5. set_max_cpu_num() assigns sysfs CPU count to int16_t max_cpu_num
     without clamping.  Systems with >32767 possible CPUs silently
     truncate to negative, causing undersized allocations.  Also makes
     max_present_cpu_num clamp consistently instead of erroring.

  6. free_idle_threads() calls free() on the thread priv without
     deep-freeing callchain cursor nodes or callchain root entries
     allocated during --idle-hist processing.  Introduces
     callchain_cursor_cleanup() for the cursor node linked list.

  7. Documents the struct perf_cpu int16_t limitation as a libperf
     ABI constraint, and creates tools/lib/perf/TODO to collect
     items that require a future ABI bump.

All require crafted or unusual perf.data inputs to trigger (except
patch 6 which is a memory leak on normal --idle-hist runs, and patch 7
which is documentation only).

Verified with gcc and clang builds, checkpatch, and perf test.

Arnaldo Carvalho de Melo (7):
  perf mmap: Fix NULL deref in aio cleanup on alloc failure
  perf stat: Introduce perf_env__get_cpu_topology() to guard NULL env->cpu
  perf c2c: Fix use-after-free in he__get_c2c_hists() error path
  perf timechart: Fix cpu2y() OOB read on untrusted CPU index
  perf tools: Fix int16_t truncation of max_cpu_num in set_max_cpu_num()
  perf sched: Free callchain nodes in idle thread cleanup
  libperf: Document struct perf_cpu int16_t ABI limitation

 tools/lib/perf/TODO                  | 22 ++++++++++++++++
 tools/lib/perf/include/perf/cpumap.h |  8 +++++-
 tools/perf/builtin-c2c.c             |  1 +
 tools/perf/builtin-sched.c           |  5 +++-
 tools/perf/builtin-stat.c            | 51 ++++++++++++++++++++----------------
 tools/perf/util/callchain.c          | 15 +++++++++++
 tools/perf/util/callchain.h          |  1 +
 tools/perf/util/cpumap.c             | 21 ++++++++++++---
 tools/perf/util/env.h                | 14 ++++++++++
 tools/perf/util/mmap.c               | 10 ++++---
 tools/perf/util/svghelper.c          | 10 ++++---
 11 files changed, 121 insertions(+), 37 deletions(-)
 create mode 100644 tools/lib/perf/TODO

Developed with AI assistance (Claude/sashiko), tagged in commits.

Thanks,

- Arnaldo