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AKwUvByLmHhVfS/vP97Fuc6SLWM+rPgBCzJQyodlV24TmSTFI92GO+qXQqiS71wIFG8RFf//3NgLmBB5uCknTXE=@vger.kernel.org X-Gm-Message-State: AFq9FYKU6BOsewc6vJWujd86EttGdcDqbx/X5963kUjAJxO7T5hkIPH3 7kPYTWuRjEkOmPkIahHMcA1L6UkcO2zrkBHRKVeylwO//dBjDKrSkFmejjEvJYJNeZLYBsCgV1k Kxs1yfQLR7g== X-Received: from dlbtv5.prod.google.com ([2002:a05:7022:3c85:b0:184:2050:3ded]) (user=irogers job=prod-delivery.src-stubby-dispatcher) by 2002:a05:701b:2718:b0:185:4ad4:3d15 with SMTP id a92af1059eb24-1854ad43d90mr7889982c88.1.1792301834096; Sat, 17 Oct 2026 22:37:14 -0700 (PDT) Date: Sat, 17 Oct 2026 22:37:04 -0700 In-Reply-To: <20261017171437.2066343-1-irogers@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20261017171437.2066343-1-irogers@google.com> X-Mailer: git-send-email 2.56.0.212.g129ede20d9-goog Message-ID: <20261018053710.2572636-1-irogers@google.com> Subject: [PATCH v3 0/6] perf bpf-filter / lock contention: Add lock_held() sample filter and RCU/SRCU support From: Ian Rogers To: irogers@google.com, acme@kernel.org, namhyung@kernel.org Cc: adrian.hunter@intel.com, james.clark@linaro.org, jolsa@kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, rcu@vger.kernel.org Content-Type: text/plain; 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 extends both `lock_held()` and `perf lock contention --use-bpf` to support RCU and SRCU, and fixes a pre-existing `lock_stat` filtering bug in `perf lock contention`. 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 (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`, `!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), 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, supporting both PMU/software events (`SEC("perf_event")`) and tracepoint events (`SEC("tracepoint")`). 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`). 6. "perf lock contention: Filter events before creating lock_stat": Fixes `report_lock_contention_begin_event()` in `builtin-lock.c` to apply `-Y`, `-L`, and `-S` filters before calling `lock_stat_findnew()`. 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 6 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 (6): 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 perf lock contention: Filter events before creating lock_stat tools/perf/Documentation/perf-lock.txt | 7 +- tools/perf/Documentation/perf-record.txt | 64 +- tools/perf/builtin-lock.c | 88 +- tools/perf/tests/parse-events.c | 121 ++ tools/perf/tests/shell/lock_contention.sh | 14 + tools/perf/tests/shell/record_bpf_filter.sh | 134 ++ tools/perf/util/bpf-filter.c | 1271 ++++++++++++++++- 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 | 171 ++- .../perf/util/bpf_skel/lock_contention.bpf.c | 448 +++--- tools/perf/util/bpf_skel/lock_data.h | 360 ++++- tools/perf/util/bpf_skel/sample-filter.h | 77 + tools/perf/util/bpf_skel/sample_filter.bpf.c | 1225 ++++++++++++++++ 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/machine.c | 11 + tools/perf/util/parse-events.c | 3 +- 20 files changed, 3741 insertions(+), 387 deletions(-) -- 2.56.0.212.g129ede20d9-goog