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charset="UTF-8" This series adds a new BPF sample filter predicate, `lock_held()` (along with `lock_held_read()` / `lock_held_shared()`, `lock_held_write()` / `lock_held_exclusive()`, 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 fixes a `bpf_link` memory leak in `perf_bpf_filter__prepare()`, enables BPF sample filters on tracepoint events (`PERF_TYPE_TRACEPOINT`), and 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 An important use-case is detecting memory allocations or direct memory reclaim occurring while kernel locks are held, which can stall lock waiters for extended periods under memory pressure: # Direct memory reclaim triggered while holding any mutex or rwsem: # perf record -a -g -e vmscan:mm_vmscan_direct_reclaim_begin \ --filter 'lock_held(mutex) || lock_held(rwsem)' -- ... # Page allocations permitted to enter direct reclaim (__GFP_DIRECT_RECLAIM) # while holding a mutex or rwsem: # perf record -a -g -e kmem:mm_page_alloc \ --filter 'gfp_flags & 0x400' \ --filter 'lock_held(mutex) || lock_held(rwsem)' -- ... # Major page faults occurring while holding a mutex or rwsem: # perf record -a -g -e major-faults \ --filter 'lock_held(mutex) || lock_held(rwsem)' -- ... Supported `` specifications match `perf lock contention`: - Global/static kernel lock symbols (e.g. `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`, `!CONFIG_UNINLINE_SPIN_UNLOCK`, `CONFIG_INLINE_*_UNLOCK*`, etc.), `_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. `configure_lock_progs()` verifies that both acquire and release entry points exist in BTF before enabling a lock family. - 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 without attaching any `fentry`/`fexit` hooks for `*_mutex`, `*_rt_mutex`, and `mmap_lock:W`), 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 LRU 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. - Cross-task semaphore signaling (`down*()` / `up()`): - Counting `struct semaphore`s do not enforce same-task ownership in the kernel: when a semaphore is used as a completion/signaling mechanism (`down()` in one task woken by `up()` in another task or interrupt handler, which proposed kernel dependency trackers like `CONFIG_DEPT` model as wait/event dependencies bounded by execution context rather than lock ownership), `fexit/down` and `fentry/up` do not pair on the same task ID. Semaphore hooks are therefore only enabled when `semaphore` or a `*_sem` symbol (such as `console_sem`) is explicitly specified, and `held_locks` uses `BPF_MAP_TYPE_LRU_HASH` so any unpaired cross-task entries are automatically evicted. - Shared `trace_event_call->prog_array` on `PERF_TYPE_TRACEPOINT`: - In `kernel/events/core.c`, `__perf_event_set_bpf_prog()` requires `BPF_PROG_TYPE_TRACEPOINT` for `PERF_TYPE_TRACEPOINT` events and attaches the program to `event->tp_event->prog_array` on the shared `trace_event_call`. Because `perf_trace_run_bpf_submit()` executes `trace_call_bpf()` before `perf_tp_event()`, returning 0 from `perf_tp_sample_filter` filters that tracepoint invocation before `perf_tp_event()` iterates `call->perf_events` (affecting concurrent `perf_event` listeners on the same tracepoint while the privileged `perf record` session is active). Patch overview (patches 1-2 are standalone fixes independent of the rest of the series): 1. "perf bpf-filter: Fix bpf_link leak by using PERF_EVENT_IOC_SET_BPF": Attaches `perf_sample_filter` directly via `PERF_EVENT_IOC_SET_BPF` in `perf_bpf_filter__prepare()`, matching the pinned filter path and avoiding leaking `struct bpf_link_perf` or double-closing `FD(evsel, x, y)`. 2. "perf bpf-filter: Support BPF sample filters on tracepoint events": Adds `SEC("tracepoint") int perf_tp_sample_filter(void *ctx)` so BPF sample filters can attach to `PERF_TYPE_TRACEPOINT` events (where `__perf_event_set_bpf_prog()` in `kernel/events/core.c` requires `BPF_PROG_TYPE_TRACEPOINT` rather than `BPF_PROG_TYPE_PERF_EVENT`). 3. "perf lock contention: Share common BPF and lock type definitions in lock_data.h": Pure refactoring moving `lock_type_table` to `util/lock-contention.c` and `LCB_F_*` flags, CO-RE structs, and common BPF lock helpers into `tools/perf/util/bpf_skel/lock_data.h`. 4. "perf lock contention: Extend get_lock_owner() for rt_mutex and mutex handoff": Extends `get_lock_owner()` in `lock_data.h` to support `rt_mutex` (`LCB_F_RT`), `CONFIG_PREEMPT_RT` mutexes, and `MUTEX_FLAG_HANDOFF`. 5. "perf bpf-filter: Add lock_held() sample filter for global mutexes": Adds the `lock_held()`, `lock_held_read()`/`lock_held_shared()`, `lock_held_write()`/`lock_held_exclusive()`, and `:R`/`:W` filter syntax and evaluates global/static kernel mutexes via direct `lock->owner` inspection. 6. "perf bpf-filter: Extend lock_held() to other kernel lock types": Extends `lock_held()` to spinlocks, rwsems, rwlocks, rt-mutexes, percpu-rwsems, and semaphores (as well as hex addresses and lock type filters) using a `held_locks` BPF LRU hash map updated by selectively attached `fentry`/`fexit` hooks. 7. "perf bpf-filter: Support per-process and semi-global locks in lock_held()": Adds support for `mmap_lock`, `siglock`, `rq_lock`, and `zone_lock`. 8. "perf bpf-filter: Support slab cache locks (&) in lock_held()": Adds support for slab cache locks prefixed with `&` (e.g. `lock_held(&dentry)`) using the `kmem_cache` BPF iterator and `slab_caches` map. 9. "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`. 10. "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()`). 11. "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`). Changes in v6: - Drop "perf lock contention: Filter events before creating lock_stat" as Arnaldo cherry-picked it. - Add an inline comment above `pin_filter_object()` in `util/bpf-filter.c` in patch 2 explaining why `bpf_object__pin()` / `bpf_object__unpin()` cannot be used when programs in `sample_filter.bpf.c` have `autoload` disabled (Namhyung). - Split the `lock_data.h` refactoring into a pure code-movement commit (patch 3) and a separate commit extending `get_lock_owner()` for `rt_mutex` and `MUTEX_FLAG_HANDOFF` (patch 4), keep `lock_syms` in its original location in `lock_contention.bpf.c`, and add a comment above `#ifdef __BPF__` in `lock_data.h` explaining that the header is shared between userspace and BPF programs (Namhyung). - Split the `lock_held()` implementation into 4 incremental commits (patches 5-8): (5) core parser, expression evaluation, and global mutex support; (6) other kernel lock types (`spinlock`, `rwsem`, `rwlock`, `rt-mutex`, `percpu-rwsem`, `semaphore`), hex addresses, and lock type filters; (7) per-process (`mmap_lock`, `siglock`) and semi-global (`rq_lock`, `zone_lock`) locks; and (8) slab cache locks (`&`) (Namhyung). - Update `is_possible_tp_filter()` in `util/parse-events.c` in patch 2 to check all tracepoint BPF sample filter terms enabled by that patch (`uid`, `gid`, `tid`, `pid`, `cpu`, `time`, `cgroup`) using word-boundary matching (`has_filter_word()`) and `!evsel__field()` so they are routed to `evsel->bpf_filters` when not matching a tracepoint format field, and extend `bpf_tp_terms[]` with `lock_held*` in patch 5. - Replace `strtailcmp(base, ...)` with `str_ends_with(base, ...)` in `prescan_one_lock_expr()` and `resolve_lock_expr()` in `util/bpf-filter.c` (patches 5, 6, and 10) so lock symbol names shorter than a tested suffix (such as `lock` vs `spinlock`, or `u_rwsem` vs `percpu_rwsem`) are not misclassified. - Use a CO-RE flavor struct `struct rt_mutex_base___new` in `lock_data.h` (patch 4) and add explicit standard C header includes (``, ``, ``, ``, ``, ``) in patches 1, 2, and 11 for musl libc compatibility. - Reject kernel text functions, module text functions, and absolute or undefined symbols when resolving lock addresses from `/proc/kallsyms`, and check for `__percpu_rwsem_rc_` in BTF so `percpu_rw_semaphore` symbols ending in `_rwsem` (such as `cgroup_threadgroup_rwsem` or `file_rwsem`) do not set `PBF_LOCK_DIRECT_RWSEM` or allow read-only mode. - Link to v5: https://lore.kernel.org/linux-perf-users/20261020205859.1080743-1-irogers@google.com/ Changes in v5: - Add patch 2 ("perf bpf-filter: Fix bpf_link leak by using PERF_EVENT_IOC_SET_BPF") attaching BPF sample filters via `ioctl(..., PERF_EVENT_IOC_SET_BPF, fd)` instead of `bpf_program__attach_perf_event_opts()`, fixing the `bpf_link` memory leak without double-closing `FD(evsel, x, y)`, and use the same attachment in patch 3 for tracepoint sample filters (Namhyung). - Expand patch 3's commit message to detail why `pin_filter_object()` and `unpin_filter_object()` replace `bpf_object__pin()` and `bpf_object__unpin()` when `autoload` is disabled on `perf_tp_sample_filter` (Namhyung). - Store the resolved lock target in `perf_bpf_filter_entry.value` (with `op` normalized to `PBF_OP_EQ` or `PBF_OP_NEQ`), keeping `struct perf_bpf_filter_entry` unchanged at 24 bytes for backwards compatibility with pinned `filters` maps. - Add a CO-RE `struct rt_mutex___old` fallback in `get_lock_owner()` in `lock_data.h` for kernels prior to v5.15, and pass baseline nesting depth to `is_rcu_trace_lock_held()` for syscall tracepoints. Changes in v4: - Move the two bugfix commits (`Filter events before creating lock_stat` and `Support BPF sample filters on tracepoint events`) to patches 1 and 2 at the start of the series for easier cherry-picking. - Reserve leading `&` strictly for slab cache locks (e.g. `lock_held(&dentry)`) so global/static lock symbols and well-known locks do not use `&` (e.g. `lock_held(cgroup_mutex)`, `lock_held_read(mmap_lock)`), matching `perf lock contention` (Namhyung). - Skip attaching `fentry`/`fexit` hooks when filtering on a specific `mutex` symbol (`*_mutex`), `rt_mutex` symbol (`*_rt_mutex`), or write-locked `mmap_lock` (`mmap_lock:W` / `lock_held_write(mmap_lock)`), evaluating them purely via direct `owner` inspection (Namhyung). - Use a CO-RE flavor struct `struct mutex___non_rt` in `get_lock_owner()` in `lock_data.h` so `GEN_VMLINUX_H=1` builds succeed on `CONFIG_PREEMPT_RT=y` kernels. - Switch `held_locks` to `BPF_MAP_TYPE_LRU_HASH`, exclude `LOCK_PROG_SEM` from `LOCK_PROG_ALL` unless `semaphore` or a `*_sem` symbol is explicitly requested, and document cross-task semaphore signaling limitations (and comparison with `CONFIG_DEPT`). - Skip `LCB_F_MUTEX | LCB_F_SPIN` in `parse_lock_type_name()`, reject read-only mode on exclusive-only lock symbol suffixes in `resolve_lock_expr()`, and check `needed_groups & supported_groups` before masking `needed_groups` in `configure_lock_progs()`. - Recursively traverse anonymous structs/unions in `btf_has_task_field()` so `lock_held(rcu)` and `lock_held(rcu-trace)` work on `CONFIG_RANDSTRUCT` kernels. Changes in v3: - Move the writer-only `rw_semaphore` check out of `get_lock_owner()` in `lock_data.h` into `is_rwsem_writer_owner()` in `sample_filter.bpf.c` so `perf lock contention -b -o` still reports reader owners when a writer contends on a reader-owned `rw_semaphore`, and scope `is_direct_lock_owner()` by lock type (`PBF_LOCK_DIRECT_MUTEX`, `PBF_LOCK_DIRECT_RWSEM`, `PBF_LOCK_DIRECT_RTMUTEX`). - Add `SEC("tracepoint") int perf_tp_sample_filter(void *ctx)` so BPF sample filters (`lock_held()`, `uid`, `gid`, etc.) can attach to `PERF_TYPE_TRACEPOINT` events (such as `kmem:mm_page_alloc` and `vmscan:mm_vmscan_direct_reclaim_begin`), check `libbpf_get_error()` when attaching, and document memory allocation / direct reclaim filtering with `lock_held()`. - Return early in `init_numa_data()` in `bpf-filter.c` when `node_data` cannot be resolved and check `node_data_addr != 0` in `do_collect_zone_lock()`. - Avoid double-counting `_raw_read_lock_irq` / `_raw_read_lock_bh` in `sample_filter.bpf.c` on `CONFIG_GENERIC_LOCKBREAK=y && !CONFIG_DEBUG_LOCK_ALLOC` kernels where they call `_raw_read_lock_irqsave()`. - Offset `rcu_state_addr` by 1 byte so it is distinct from `&rcu_state.node[0].lock` at offset 0 of `rcu_state`, and pass `bool is_rcu` to `do_contention_end()` in `lock_contention.bpf.c` so `tp_btf/contention_end` and RCU/SRCU `fexit` hooks never cross-match timestamp maps. Changes in v2: - Guard `BPF_CORE_READ(mutex, owner.counter)` with `bpf_core_field_exists` and fall back to `struct rt_mutex_base` in `get_lock_owner()` so CO-RE relocation succeeds on `CONFIG_PREEMPT_RT=y` kernels. - Add `CONFIG_DEBUG_LOCK_ALLOC=y` lock entry points (`_mutex_lock_nest_lock`, `_mutex_lock_killable`, `_mutex_trylock_nest_lock`, `_down_write_nest_lock`, `_raw_spin_lock_nest_lock`, `_rt_mutex_lock_nest_lock`) to `sample_filter.bpf.c` and `lock_progs[]`. - Verify in `supported_lock_prog_groups()` that both acquire and all unlock BTF entry points exist for a lock family before enabling its tracing hooks, preventing acquire-only attachment when spinlock/rwlock unlock functions are inlined. - Enable `LOCK_PROG_PERCPU_RWSEM` alongside `LOCK_PROG_RWSEM_WRITE` when a symbol name ends in `rwsem` (such as `cgroup_threadgroup_rwsem`). - Gate `record_lock_acquired(ctx, LCB_F_READ)` in `fexit_downgrade_write` on `track_rwsem_read` and verify non-zero read/write counts in `record_lock_released_addr()` before decrementing aggregate slab/type counts. - Adjust stack skip depth by 2 for `fentry` RCU/SRCU programs in `lock_contention.bpf.c` and recognize `synchronize_rcu*`, `synchronize_srcu*`, `rcu_barrier`, and `srcu_barrier` in `machine__is_lock_function()`. - Add patch fixing `report_lock_contention_begin_event()` to check type, address, and callstack filters before creating `lock_stat` entries. Assisted-by: Antigravity:gemini-3.1-pro Ian Rogers (11): perf bpf-filter: Fix bpf_link leak by using PERF_EVENT_IOC_SET_BPF perf bpf-filter: Support BPF sample filters on tracepoint events perf lock contention: Share common BPF and lock type definitions in lock_data.h perf lock contention: Extend get_lock_owner() for rt_mutex and mutex handoff perf bpf-filter: Add lock_held() sample filter for global mutexes perf bpf-filter: Extend lock_held() to other kernel lock types perf bpf-filter: Support per-process and semi-global locks in lock_held() perf bpf-filter: Support slab cache locks (&) in lock_held() 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 | 74 +- 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 | 142 ++ tools/perf/util/bpf-filter.c | 1475 ++++++++++++++++- tools/perf/util/bpf-filter.h | 13 + tools/perf/util/bpf-filter.l | 31 +- tools/perf/util/bpf-filter.y | 47 +- tools/perf/util/bpf_lock_contention.c | 174 +- .../perf/util/bpf_skel/lock_contention.bpf.c | 431 ++--- tools/perf/util/bpf_skel/lock_data.h | 394 ++++- tools/perf/util/bpf_skel/sample-filter.h | 80 + tools/perf/util/bpf_skel/sample_filter.bpf.c | 1241 ++++++++++++++ tools/perf/util/bpf_skel/vmlinux/vmlinux.h | 7 + tools/perf/util/lock-contention.c | 23 + tools/perf/util/lock-contention.h | 15 + tools/perf/util/machine.c | 11 + tools/perf/util/parse-events.c | 40 +- 20 files changed, 4008 insertions(+), 359 deletions(-) -- 2.56.0.307.g5fe7bd680c-goog