Merge branch 'veristat-memory-accounting-for-bpf-programs'

Eduard Zingerman says:

====================
veristat: memory accounting for bpf programs

When working on the verifier, it is sometimes interesting to know how a
particular change affects memory consumption. This patch-set modifies
veristat to provide such information. As a collateral, kernel needs an
update to make allocations reachable from BPF program load accountable
in memcg statistics.

Here is a sample output:

  Program          Peak states  Peak memory (MiB)
  ---------------  -----------  -----------------
  lavd_select_cpu         2153                 43
  lavd_enqueue            1982                 41
  lavd_dispatch           3480                 28

Technically, this is implemented by creating and entering a new cgroup
at the start of veristat execution. The difference between values from
cgroup "memory.peak" file before and after bpf_object__load() is used
as a metric.

To minimize measurements jitter data is collected in megabytes.

Changelog:
v2: https://lore.kernel.org/bpf/20250612130835.2478649-1-eddyz87@gmail.com/
v2 -> v3:
- bpf_verifier_state->jmp_history and
  bpf_verifier_env->explored_states allocations are switched from
  GFP_USER to GFP_KERNEL_ACCOUNT (Andrii, Alexei);
- veristat.c:STR macro removed, PATH_MAX-1 == 4095 is hard-coded in
  scanf format strings (Andrii);
- env->{orig,stat}_cgroup size changed to PATH_MAX (Andrii);
- snprintf_trunc() is removed, flag -Wno-format-truncation
  is added to CFLAGS for veristat.o when compiled with gcc;

v1: https://lore.kernel.org/bpf/20250605230609.1444980-1-eddyz87@gmail.com/
v1 -> v2:
- a single cgroup, created at the beginning of execution, is now used
  for measurements (Andrii, Mykyta);
- cgroup namespace is not created, as it turned out to be useless
  (Andrii);
- veristat no longer mounts cgroup fs or changes subtree_control,
  instead it looks for an existing mount point and reports an error if
  memory.peak file can't be opened (Andrii, Alexei);
- if 'mem_peak' statistics is not enabled, veristat skips cgroup
  setup;
- code sharing with cgroup_helpers.c was considered but was decided
  against to simplify veristat github sync.
====================

Link: https://patch.msgid.link/20250613072147.3938139-1-eddyz87@gmail.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>