This series adds a new BPF sample filter predicate, `lock_held(<lock>)`
(along with `lock_held_read(<lock>)` / `lock_held_shared(<lock>)`,
`lock_held_write(<lock>)` / `lock_held_exclusive(<lock>)`, and `:R` / `:W`
mode suffixes), to `perf record --filter`, allowing perf event samples to
be recorded only when a specified kernel lock is held (or not held with
`!`) by the running kernel thread or CPU. It also extends both
`lock_held()` and `perf lock contention --use-bpf` to support RCU and
SRCU.
For example:
# perf record -a -g -e cycles --filter 'lock_held(&cgroup_mutex)' -- ...
# perf record -a -g -e cycles --filter 'lock_held_read(&mmap_lock)' -- ...
# perf record -a -g -e cycles --filter 'lock_held(&mmap_lock:W)' -- ...
# perf record -a -g -e cycles --filter 'lock_held_read(rcu)' -- ...
# perf lock contention -a -b -Y rcu,srcu -- sleep 1
Supported `<lock>` specifications match `perf lock contention`:
- Global/static kernel lock symbols (with or without leading `&`, e.g.
`lock_held(&cgroup_mutex)` or `lock_held(cgroup_mutex)`)
- Hexadecimal kernel lock addresses
- Slab cache names prefixed with `&` (e.g. `lock_held(&dentry)`,
`lock_held_read(&dentry)`)
- Well-known per-process, semi-global, and RCU locks: `mmap_lock`,
`siglock`, `rq_lock`, `zone_lock`, `rcu`, `rcu-trace`
- Lock types and flags: `mutex`, `spinlock`, `rwsem`, `rwsem:R`,
`rwsem:W`, `rwlock`, `rwlock:R`, `rwlock:W`, `rt-mutex`,
`percpu-rwsem`, `pcpu-sem:W`, `srcu`, `srcu:R`, `srcu:W`, `rcu:R`,
`rcu:W`, `semaphore`
Limitations and weaknesses in determining whether a lock is held:
- Inlined lock/unlock operations:
- When the kernel is configured to inline spinlock or rwlock operations
(`CONFIG_INLINE_SPIN_LOCK`, `CONFIG_INLINE_READ_LOCK`,
`CONFIG_INLINE_WRITE_LOCK`, etc., which are enabled on many
`!CONFIG_PREEMPT_RT` / `!CONFIG_PROVE_LOCKING` builds unless
`CONFIG_UNINLINE_SPIN_UNLOCK` or lockdep/preemption forces them out of
line), `_raw_spin_lock*` / `_raw_spin_unlock*` and
`_raw_read_lock*` / `_raw_write_lock*` are inlined into callers and
have no BTF function entry points for `fentry`/`fexit` to attach to.
- Fast-path `percpu_down_read()` / `percpu_up_read()` and
`srcu_read_lock_fast()` / `srcu_read_unlock_fast()` are inlined
per-CPU counter increments without function calls, so only
`percpu_down_write()` / `percpu_up_write()` and out-of-line
`__srcu_read_lock*()` / `__srcu_read_unlock*()` can be hooked.
- On `!CONFIG_PREEMPT_RCU` kernels, `rcu_read_lock()` compiles to
`preempt_disable()` and does not maintain
`current->rcu_read_lock_nesting` in `task_struct`, so `lock_held(rcu)`
read-side inspection requires `CONFIG_PREEMPT_RCU`.
- Lack of an inspectable owner field on non-exclusive / spinning locks:
- While `struct mutex`, `struct rt_mutex`, and write-locked
`struct rw_semaphore` store the owning `task_struct *` in `lock->owner`
(allowing `perf_sample_filter` to inspect kernel memory directly on
sample overflow when filtering by lock address), spinlocks, rwlocks,
semaphores, SRCU, and reader-locked `rw_semaphore`s (where
`__up_read()` does not clear `sem->owner` when `!CONFIG_DEBUG_RWSEMS`)
do not maintain an authoritative per-task owner pointer.
- Tracking these locks (as well as slab-cache and lock-type filters)
relies on `fexit` (acquire) and `fentry` (release) BPF hooks
maintaining the `held_locks` BPF hash map:
- Any such lock already held before `perf record` attaches its BPF
programs will not be present in `held_locks` until it is released
and re-acquired.
- The attached `fentry`/`fexit` hooks execute on every kernel lock
acquire and release for the hooked lock family across the system,
adding tracing overhead outside of perf sample handling.
Patch overview:
1. "perf lock contention: Share common BPF and lock type definitions in
lock_data.h": Moves `lock_type_table` to `util/lock-contention.c` and
`LCB_F_*` flags, CO-RE structs, and common BPF lock helpers
(`get_lock_owner`, `get_current_mmap_lock`, `get_current_siglock`,
`get_lock_addr`, `check_lock_type`, `do_collect_lock_syms`,
`do_slab_cache_iter`) into `tools/perf/util/bpf_skel/lock_data.h`.
2. "perf bpf-filter: Add lock_held() sample filter": Implements
`lock_held()`, `lock_held_read()`/`lock_held_shared()`,
`lock_held_write()`/`lock_held_exclusive()`, and `:R`/`:W` mode
suffixes using direct lock owner inspection where possible (`mutex`,
`rt_mutex`, write-locked `rw_semaphore`) and a `held_locks` BPF map
updated by selectively attached `fentry`/`fexit` hooks.
3. "perf test: Add tests for lock_held() BPF sample filter": Adds unit
tests in `tests/parse-events.c` and shell tests in
`tests/shell/record_bpf_filter.sh`.
4. "perf bpf-filter: Extend lock_held() to support RCU, Tasks Trace RCU,
and SRCU": Supports `rcu` (`rcu:R` via direct
`current->rcu_read_lock_nesting` inspection with zero tracing hooks;
`rcu:W` via `synchronize_rcu*()` / `rcu_barrier()` hooks),
`rcu-trace` (via `current->trc_reader_nesting`), and `srcu`
(`srcu:R` via `__srcu_read_lock*` / `__srcu_read_unlock*`; `srcu:W`
via `synchronize_srcu*()` / `srcu_barrier()`).
5. "perf lock contention: Extend BPF lock contention to RCU and SRCU":
Extends `perf lock contention --use-bpf` to track RCU and SRCU
grace-period and barrier waits (`-Y rcu`, `-Y srcu`, `-L rcu`).
Assisted-by: Antigravity:gemini-3.1-pro
Ian Rogers (5):
perf lock contention: Share common BPF and lock type definitions in
lock_data.h
perf bpf-filter: Add lock_held() sample filter
perf test: Add tests for lock_held() BPF sample filter
perf bpf-filter: Extend lock_held() to support RCU, Tasks Trace RCU,
and SRCU
perf lock contention: Extend BPF lock contention to RCU and SRCU
tools/perf/Documentation/perf-lock.txt | 7 +-
tools/perf/Documentation/perf-record.txt | 51 +-
tools/perf/builtin-lock.c | 27 -
tools/perf/tests/parse-events.c | 121 ++
tools/perf/tests/shell/lock_contention.sh | 14 +
tools/perf/tests/shell/record_bpf_filter.sh | 119 ++
tools/perf/util/bpf-filter.c | 1070 ++++++++++++++++-
tools/perf/util/bpf-filter.h | 13 +
tools/perf/util/bpf-filter.l | 31 +-
tools/perf/util/bpf-filter.y | 46 +-
tools/perf/util/bpf_lock_contention.c | 167 ++-
.../perf/util/bpf_skel/lock_contention.bpf.c | 410 +++----
tools/perf/util/bpf_skel/lock_data.h | 360 +++++-
tools/perf/util/bpf_skel/sample-filter.h | 71 ++
tools/perf/util/bpf_skel/sample_filter.bpf.c | 1051 ++++++++++++++++
tools/perf/util/bpf_skel/vmlinux/vmlinux.h | 7 +
tools/perf/util/lock-contention.c | 22 +
tools/perf/util/lock-contention.h | 15 +
tools/perf/util/parse-events.c | 3 +-
19 files changed, 3273 insertions(+), 332 deletions(-)
--
2.56.0.212.g129ede20d9-goog
