From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9AEC4407CD8; Wed, 20 May 2026 18:50:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779303010; cv=none; b=u7c0t3fDo79uqJ+PpaquO6HDhRTTNWubkVWH2rZJucYWAIf80b4zF6zVa4wtBq/GMtDF9hG5TWBKW+yPqjREU4UWGGBhKXx7UuvwczJdjYrb/dXOauSRTsdRjpA7/k9KXF9Bv2hegLanIg41Tx25LwOzPlWmltAW5JiAsXBLPJY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779303010; c=relaxed/simple; bh=+QjRjOIYSxwOhZM9tWkY+qyaunWJj+bbW8RN3AD9sYY=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=nThzYIDVxEioaQZotUYyDks6P4o3ENPXHrX1uvSTVTcbGzdSyLTIeKd+saJavr5PxmAOzIjAlz2077sqDqyUaTUbfPI6caYxnUKVx7Mb1JCqaSM9l4T5mMeaiAOb9PF414mSdzlNrwsxCkbadwwvfQnpyI0w3Qboc5P6lXkhlmA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZUnKIgwb; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZUnKIgwb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 05B461F0089F; Wed, 20 May 2026 18:49:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779302999; bh=jygDceG30LUq+hbqus2XeFHvbPtOFQakWAqYsRXmO/k=; h=Date:From:To:Cc:Subject:References; b=ZUnKIgwbzwLbDGQp78LIep0m697U9ZzxtGobybxEy9rTKWIadU8MllJy0Mp3Ylke9 mRphhWEzgjS0io6XVokeEZHWKoDTqacv+bMiEQl7cHZ/sxhEG2SJMBa5xg7IMEj42v LERXYwOKi/wG+HRCSfy1k74hmiEH2FxBHic5dKrFg6LQQ//oNz+JOns8GVknVqui9U sPZaHYNI4syBr2Ed+6mpaURkPIQDJS55DMBVYBJo1b67KdlzlOSfnsH+RkX9KIqoyZ A5C7fiLsGK6yLriDeeEbp792j22VEzFqzjtw80PM94mAiywbRE+VAgxGq3hUUPrwxU kbNnnq1c6C8mw== Received: from rostedt by gandalf with local (Exim 4.99.2) (envelope-from ) id 1wPlzm-00000004qVJ-2UWl; Wed, 20 May 2026 14:50:18 -0400 Message-ID: <20260520185018.470465795@kernel.org> User-Agent: quilt/0.69 Date: Wed, 20 May 2026 14:49:48 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mathieu Desnoyers , Catalin Marinas , Will Deacon , Ian Rogers Subject: [PATCH v20 10/10] ring-buffer: Show persistent buffer dropped events in trace_pipe file References: <20260520184938.749337513@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: Steven Rostedt When the persistent ring buffer is validated on boot up, if a subbuffer is deemed invalid, it resets the buffer and continues. Have the code preserve the RB_MISSED_EVENTS flag in the commit portion of the subbuffer header and pass that back so that the trace_pipe file can show the missed events like the trace file does. For example: <...>-1242 [005] d.... 4429.120116: page_fault_user: address=0x7ffaebb6e728 ip=0x7ffaeb9d4960 error_code=0x7 <...>-1242 [005] ..... 4429.120124: mm_page_alloc: page=00000000055254f3 pfn=0x1373bd order=0 migratetype=1 gfp_flags=GFP_HIGHUSER_MOVABLE|__GFP_COMP <...>-1242 [005] d..2. 4429.120132: tlb_flush: pages:1 reason:local MM shootdown (3) CPU:5 [LOST EVENTS] <...>-1242 [005] d.... 4429.120661: page_fault_user: address=0x55ba7c2d0944 ip=0x55ba7c20cd02 error_code=0x7 <...>-1242 [005] ..... 4429.120669: mm_page_alloc: page=0000000005a02500 pfn=0x12b6e4 order=0 migratetype=1 gfp_flags=GFP_HIGHUSER_MOVABLE|__GFP_COMP <...>-1242 [005] d..2. 4429.120680: tlb_flush: pages:1 reason:local MM shootdown (3) Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 57 +++++++++++++++++++++++--------------- 1 file changed, 35 insertions(+), 22 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9cdbee171cdc..f42d2176b92c 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5794,6 +5794,7 @@ __rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) struct buffer_page *reader = NULL; unsigned long overwrite; unsigned long flags; + int missed_events = 0; int nr_loops = 0; bool ret; @@ -5894,6 +5895,9 @@ __rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) if (!ret) goto spin; + if (rb_page_commit(reader) & RB_MISSED_EVENTS) + missed_events = -1; + if (cpu_buffer->ring_meta) rb_update_meta_reader(cpu_buffer, reader); @@ -5958,6 +5962,8 @@ __rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) */ smp_rmb(); + if (!cpu_buffer->lost_events) + cpu_buffer->lost_events = missed_events; return reader; } @@ -7059,6 +7065,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer, struct buffer_page *reader; long missed_events; unsigned int commit; + unsigned int size; unsigned int read; u64 save_timestamp; bool force_memcpy; @@ -7094,7 +7101,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer, event = rb_reader_event(cpu_buffer); read = reader->read; - commit = rb_page_size(reader); + commit = rb_page_commit(reader); + size = rb_page_size(reader); /* Check if any events were dropped */ missed_events = cpu_buffer->lost_events; @@ -7108,13 +7116,14 @@ int ring_buffer_read_page(struct trace_buffer *buffer, * we must copy the data from the page to the buffer. * Otherwise, we can simply swap the page with the one passed in. */ - if (read || (len < (commit - read)) || + if (read || (len < (size - read)) || cpu_buffer->reader_page == cpu_buffer->commit_page || force_memcpy) { struct buffer_data_page *rpage = cpu_buffer->reader_page->page; unsigned int rpos = read; unsigned int pos = 0; - unsigned int size; + unsigned int event_size; + unsigned int flags = 0; /* * If a full page is expected, this can still be returned @@ -7123,19 +7132,23 @@ int ring_buffer_read_page(struct trace_buffer *buffer, * the reader page. */ if (full && - (!read || (len < (commit - read)) || + (!read || (len < (size - read)) || cpu_buffer->reader_page == cpu_buffer->commit_page)) return -1; - if (len > (commit - read)) - len = (commit - read); + if (len > (size - read)) + len = (size - read); /* Always keep the time extend and data together */ - size = rb_event_ts_length(event); + event_size = rb_event_ts_length(event); - if (len < size) + if (len < event_size) return -1; + if (commit & RB_MISSED_EVENTS) { + printk("MISSED\n"); + flags = RB_MISSED_EVENTS; } + /* save the current timestamp, since the user will need it */ save_timestamp = cpu_buffer->read_stamp; @@ -7147,25 +7160,25 @@ int ring_buffer_read_page(struct trace_buffer *buffer, * one or two events. * We have already ensured there's enough space if this * is a time extend. */ - size = rb_event_length(event); - memcpy(dpage->data + pos, rpage->data + rpos, size); + event_size = rb_event_length(event); + memcpy(dpage->data + pos, rpage->data + rpos, event_size); - len -= size; + len -= event_size; rb_advance_reader(cpu_buffer); rpos = reader->read; - pos += size; + pos += event_size; - if (rpos >= commit) + if (rpos >= event_size) break; event = rb_reader_event(cpu_buffer); /* Always keep the time extend and data together */ - size = rb_event_ts_length(event); - } while (len >= size); + event_size = rb_event_ts_length(event); + } while (len >= event_size); /* update dpage */ - local_set(&dpage->commit, pos); + local_set(&dpage->commit, pos | flags); dpage->time_stamp = save_timestamp; /* we copied everything to the beginning */ @@ -7197,7 +7210,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer, cpu_buffer->lost_events = 0; - commit = rb_data_page_commit(dpage); + size = rb_data_page_size(dpage); /* * Set a flag in the commit field if we lost events */ @@ -7207,11 +7220,11 @@ int ring_buffer_read_page(struct trace_buffer *buffer, * missed events, then record it there. */ if (missed_events > 0 && - buffer->subbuf_size - commit >= sizeof(missed_events)) { - memcpy(&dpage->data[commit], &missed_events, + buffer->subbuf_size - size >= sizeof(missed_events)) { + memcpy(&dpage->data[size], &missed_events, sizeof(missed_events)); local_add(RB_MISSED_STORED, &dpage->commit); - commit += sizeof(missed_events); + size += sizeof(missed_events); } local_add(RB_MISSED_EVENTS, &dpage->commit); } @@ -7219,8 +7232,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer, /* * This page may be off to user land. Zero it out here. */ - if (commit < buffer->subbuf_size) - memset(&dpage->data[commit], 0, buffer->subbuf_size - commit); + if (size < buffer->subbuf_size) + memset(&dpage->data[size], 0, buffer->subbuf_size - size); return read; } -- 2.53.0