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AJvYcCW8ZJ4LF8uxRIUIxTxRob9mtzS2xoo01EOPEKs8TpiWcLMdWP9izcmVRl8pBfhxZQe305XeMcZ0BL55+SCiPon1dXNyiXdbvDj6Dohc X-Gm-Message-State: AOJu0YywSP0QD9wlpWJghJUBwACz01bjR0YAZ/LzMnDJV3opCE3WF9G1 s8VTtESLnR6+QWiq48AtlGByZzdJVHYBhMSbb2wRLCoQEJEGMRyZkP3Ceth3RUmG5cg0D5FZbZo pKQMCo6qv6myN6lFXJw== X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a05:690c:b8b:b0:604:4c5:7dc8 with SMTP id ck11-20020a05690c0b8b00b0060404c57dc8mr2160949ywb.8.1707825048353; Tue, 13 Feb 2024 03:50:48 -0800 (PST) Date: Tue, 13 Feb 2024 11:49:39 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.43.0.687.g38aa6559b0-goog Message-ID: <20240213114945.3528801-1-vdonnefort@google.com> Subject: [PATCH v17 0/6] Introducing trace buffer mapping by user-space From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, Vincent Donnefort X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1790784378091153679 X-GMAIL-MSGID: 1790784378091153679 The tracing ring-buffers can be stored on disk or sent to network without any copy via splice. However the later doesn't allow real time processing of the traces. A solution is to give userspace direct access to the ring-buffer pages via a mapping. An application can now become a consumer of the ring-buffer, in a similar fashion to what trace_pipe offers. Support for this new feature can already be found in libtracefs from version 1.8, when built with EXTRA_CFLAGS=-DFORCE_MMAP_ENABLE. Vincent v16 -> v17: * Documentation and comments improvements. * Create get/put_snapshot_map() for clearer code. * Replace kzalloc with kcalloc. * Fix -ENOMEM handling in rb_alloc_meta_page(). * Move flush(cpu_buffer->reader_page) behind the reader lock. * Move all inc/dec of cpu_buffer->mapped behind reader lock and buffer mutex. (removes READ_ONCE/WRITE_ONCE accesses). v15 -> v16: * Add comment for the dcache flush. * Remove now unnecessary WRITE_ONCE for the meta-page. v14 -> v15: * Add meta-page and reader-page flush. Intends to fix the mapping for VIVT and aliasing-VIPT data caches. * -EPERM on VM_EXEC. * Fix build warning !CONFIG_TRACER_MAX_TRACE. v13 -> v14: * All cpu_buffer->mapped readers use READ_ONCE (except for swap_cpu) * on unmap, sync meta-page teardown with the reader_lock instead of the synchronize_rcu. * Add a dedicated spinlock for trace_array ->snapshot and ->mapped. (intends to fix a lockdep issue) * Add kerneldoc for flags and Reserved fields. * Add kselftest for snapshot/map mutual exclusion. v12 -> v13: * Swap subbufs_{touched,lost} for Reserved fields. * Add a flag field in the meta-page. * Fix CONFIG_TRACER_MAX_TRACE. * Rebase on top of trace/urgent. * Add a comment for try_unregister_trigger() v11 -> v12: * Fix code sample mmap bug. * Add logging in sample code. * Reset tracer in selftest. * Add a refcount for the snapshot users. * Prevent mapping when there are snapshot users and vice versa. * Refine the meta-page. * Fix types in the meta-page. * Collect Reviewed-by. v10 -> v11: * Add Documentation and code sample. * Add a selftest. * Move all the update to the meta-page into a single rb_update_meta_page(). * rb_update_meta_page() is now called from ring_buffer_map_get_reader() to fix NOBLOCK callers. * kerneldoc for struct trace_meta_page. * Add a patch to zero all the ring-buffer allocations. v9 -> v10: * Refactor rb_update_meta_page() * In-loop declaration for foreach_subbuf_page() * Check for cpu_buffer->mapped overflow v8 -> v9: * Fix the unlock path in ring_buffer_map() * Fix cpu_buffer cast with rb_work_rq->is_cpu_buffer * Rebase on linux-trace/for-next (3cb3091138ca0921c4569bcf7ffa062519639b6a) v7 -> v8: * Drop the subbufs renaming into bpages * Use subbuf as a name when relevant v6 -> v7: * Rebase onto lore.kernel.org/lkml/20231215175502.106587604@goodmis.org/ * Support for subbufs * Rename subbufs into bpages v5 -> v6: * Rebase on next-20230802. * (unsigned long) -> (void *) cast for virt_to_page(). * Add a wait for the GET_READER_PAGE ioctl. * Move writer fields update (overrun/pages_lost/entries/pages_touched) in the irq_work. * Rearrange id in struct buffer_page. * Rearrange the meta-page. * ring_buffer_meta_page -> trace_buffer_meta_page. * Add meta_struct_len into the meta-page. v4 -> v5: * Trivial rebase onto 6.5-rc3 (previously 6.4-rc3) v3 -> v4: * Add to the meta-page: - pages_lost / pages_read (allow to compute how full is the ring-buffer) - read (allow to compute how many entries can be read) - A reader_page struct. * Rename ring_buffer_meta_header -> ring_buffer_meta * Rename ring_buffer_get_reader_page -> ring_buffer_map_get_reader_page * Properly consume events on ring_buffer_map_get_reader_page() with rb_advance_reader(). v2 -> v3: * Remove data page list (for non-consuming read) ** Implies removing order > 0 meta-page * Add a new meta page field ->read * Rename ring_buffer_meta_page_header into ring_buffer_meta_header v1 -> v2: * Hide data_pages from the userspace struct * Fix META_PAGE_MAX_PAGES * Support for order > 0 meta-page * Add missing page->mapping. Vincent Donnefort (6): ring-buffer: Zero ring-buffer sub-buffers ring-buffer: Introducing ring-buffer mapping functions tracing: Add snapshot refcount tracing: Allow user-space mapping of the ring-buffer Documentation: tracing: Add ring-buffer mapping ring-buffer/selftest: Add ring-buffer mapping test Documentation/trace/index.rst | 1 + Documentation/trace/ring-buffer-map.rst | 106 +++++ include/linux/ring_buffer.h | 7 + include/uapi/linux/trace_mmap.h | 48 +++ kernel/trace/ring_buffer.c | 385 +++++++++++++++++- kernel/trace/trace.c | 234 ++++++++++- kernel/trace/trace.h | 9 +- kernel/trace/trace_events_trigger.c | 58 ++- tools/testing/selftests/ring-buffer/Makefile | 8 + tools/testing/selftests/ring-buffer/config | 2 + .../testing/selftests/ring-buffer/map_test.c | 273 +++++++++++++ 11 files changed, 1085 insertions(+), 46 deletions(-) create mode 100644 Documentation/trace/ring-buffer-map.rst create mode 100644 include/uapi/linux/trace_mmap.h create mode 100644 tools/testing/selftests/ring-buffer/Makefile create mode 100644 tools/testing/selftests/ring-buffer/config create mode 100644 tools/testing/selftests/ring-buffer/map_test.c base-commit: ca185770db914869ff9fe773bac5e0e5e4165b83