From nobody Mon Feb 9 11:34:03 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 0C17F1F37D3; Sun, 1 Feb 2026 03:29:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769916550; cv=none; b=Ru/GDurrsBPxfuGWpqxPUJRKnHKRAkgyxBXF2CyBPqg3xMcLe0lkk3jqzHed9x1XqlrdZvAZIcMuMo2uNn3+oAD79PSsHdk2VPSu9cdMAdB8uigGzdbvhXC8dTDCJ7HgLM29uxF1RnGuc+d12zXb/qop/+vWmSwOQdDNk4RxvCA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769916550; c=relaxed/simple; bh=YQL7l01WmvmK7If7bIbiNydjrUoMH+8UyFa2Eop9bCU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Nrw2/gufhTMNam5Outlt0kdbFCPgZuj1XVoB2zIi+2UsQn8FxgrFIWXl2GUEyunEWi6bGoOaaW5CL/IlJNiGpbSYBQPcdTdiKAW7l7Fmy8lD//aIsbm5Hi9bGAlLthxGEjLN74J5W+S01oQeG3OasBH+qLP4TKgyrt/sxH3U7VQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WW/79627; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WW/79627" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BF55EC4CEF7; Sun, 1 Feb 2026 03:29:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769916549; bh=YQL7l01WmvmK7If7bIbiNydjrUoMH+8UyFa2Eop9bCU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WW/79627xL3kywna44rDXHjBbMVyZ6XvQsnpWOVYvZHGG6lIkCasFO5vFslbs1i40 s7qz/sU4obQ7h+NmxP+lpIuRcCOviAApkTh9FTE6hHOBOV2AFU1PiqJ4myWsCBa2Zt 7OttVNDccM4xnidFZEdf0PZ9ycGE1VT3tbbNyJg+78WahLI3oEtMqPP8Z/c8vnipl9 IM6bIl8Qp9GzC5hSDjVKRlFrp6eY0WSV3/xx+c+uPerl2WNbhHxitNGrylmcVxv/q1 3FDnGZkn29fCpiti5ZE00TJXeiO3w8cfP9ATdEuF7UfzI6qkHNM/QDcrr2sckZflO9 NnmNIYX2UQAZQ== From: "Masami Hiramatsu (Google)" To: Steven Rostedt Cc: Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: [PATCH v6 1/4] tracing: Reset last_boot_info if ring buffer is reset Date: Sun, 1 Feb 2026 12:29:07 +0900 Message-ID: <176991654703.4025429.9641092475053587709.stgit@mhiramat.tok.corp.google.com> X-Mailer: git-send-email 2.53.0.rc1.225.gd81095ad13-goog In-Reply-To: <176991653525.4025429.12655335935351822711.stgit@mhiramat.tok.corp.google.com> References: <176991653525.4025429.12655335935351822711.stgit@mhiramat.tok.corp.google.com> User-Agent: StGit/0.19 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" Content-Transfer-Encoding: quoted-printable From: Masami Hiramatsu (Google) Commit 32dc0042528d ("tracing: Reset last-boot buffers when reading out all cpu buffers") resets the last_boot_info when user read out all data via trace_pipe* files. But it is not reset when user resets the buffer from other files. (e.g. write `trace` file) Reset it when the corresponding ring buffer is reset too. Fixes: 32dc0042528d ("tracing: Reset last-boot buffers when reading out all= cpu buffers") Signed-off-by: Masami Hiramatsu (Google) --- kernel/trace/trace.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 396d59202438..5c3e4a554143 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4891,6 +4891,8 @@ static int tracing_single_release_tr(struct inode *in= ode, struct file *file) return single_release(inode, file); } =20 +static bool update_last_data_if_empty(struct trace_array *tr); + static int tracing_open(struct inode *inode, struct file *file) { struct trace_array *tr =3D inode->i_private; @@ -4915,6 +4917,8 @@ static int tracing_open(struct inode *inode, struct f= ile *file) tracing_reset_online_cpus(trace_buf); else tracing_reset_cpu(trace_buf, cpu); + + update_last_data_if_empty(tr); } =20 if (file->f_mode & FMODE_READ) { @@ -5981,6 +5985,7 @@ tracing_set_trace_read(struct file *filp, char __user= *ubuf, int tracer_init(struct tracer *t, struct trace_array *tr) { tracing_reset_online_cpus(&tr->array_buffer); + update_last_data_if_empty(tr); return t->init(tr); } =20 @@ -7799,6 +7804,7 @@ int tracing_set_clock(struct trace_array *tr, const c= har *clockstr) ring_buffer_set_clock(tr->max_buffer.buffer, trace_clocks[i].func); tracing_reset_online_cpus(&tr->max_buffer); #endif + update_last_data_if_empty(tr); =20 if (tr->scratch && !(tr->flags & TRACE_ARRAY_FL_LAST_BOOT)) { struct trace_scratch *tscratch =3D tr->scratch; @@ -8036,6 +8042,7 @@ tracing_snapshot_write(struct file *filp, const char = __user *ubuf, size_t cnt, tracing_reset_online_cpus(&tr->max_buffer); else tracing_reset_cpu(&tr->max_buffer, iter->cpu_file); + update_last_data_if_empty(tr); } break; } From nobody Mon Feb 9 11:34:03 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 873A91F936; Sun, 1 Feb 2026 03:29:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769916557; cv=none; b=FkKv+kHNXmKLYRAAWlU7uu7Mo2k9LnCWWLRwJzjLLpBwButntLA0PhQ8lJrk905b4rPdLZcAoLE9LMwSTLcKWL13yaQKLDGJhoCZnoioqtF9tAge/F2BJL9vdD8QIabCxN9v6JEj6Ojg+dwpeir6rTDmK7Qaa4HUrSdGJFl8iAo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769916557; c=relaxed/simple; bh=xvSFkVSSG0jW5eAJjXX09hvhPUJmHkArft8HRfGHAj4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=hQYkwKpIA2KCph+3HfxKA2QZwnYUFsjzIGGj9+y5OuEReUZw5zslSAVW0H028lStLfprwZ4QI5H1BwyC1Sfh+HPWiwCPZemrSjOo9ypK957Nva2ZQmTOL1KU5xXs0PGzPdQm3aAe7pEoRSNHY/Unbf8uWi3v2GsO9xBKifNNC1Y= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OzgOlb1P; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OzgOlb1P" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 765BBC4CEF7; Sun, 1 Feb 2026 03:29:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769916557; bh=xvSFkVSSG0jW5eAJjXX09hvhPUJmHkArft8HRfGHAj4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OzgOlb1PoptsDAgmTCXDnLD/cKBtPsw52ZOYBBv/l6Ry1VoEhcYz2HPEbCcDhE0dd 47Be1XRw4IXn+bjFZbhZ1TfbJCfUXzsJ/PYn+7EkcjQsx3FEBU9N0oF3Pz1UnNPbui 9E177pXKZEZb9fGWS9h5FXBgKEU4MYnqVdXRTK4A7wGoogm60oOE7hyUpOo3S8WFL1 OeyMmSjCslzFFifaXOrlaGMieP/Qsqf/LQa3CVUR+xOXCFyw8i042A97d1E8RgKfUa 7t125ubOPOoopKqrB4mlS2VHaGfAeP9nuQwAf8HVE8ESztWW7yY7h4uohkn64J0wOS R40cFBmD3Of1g== From: "Masami Hiramatsu (Google)" To: Steven Rostedt Cc: Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: [PATCH v6 2/4] tracing: Make the backup instance non-reusable Date: Sun, 1 Feb 2026 12:29:15 +0900 Message-ID: <176991655479.4025429.105619035638065215.stgit@mhiramat.tok.corp.google.com> X-Mailer: git-send-email 2.53.0.rc1.225.gd81095ad13-goog In-Reply-To: <176991653525.4025429.12655335935351822711.stgit@mhiramat.tok.corp.google.com> References: <176991653525.4025429.12655335935351822711.stgit@mhiramat.tok.corp.google.com> User-Agent: StGit/0.19 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" Content-Transfer-Encoding: quoted-printable From: Masami Hiramatsu (Google) Since there is no reason to reuse the backup instance, make it readonly (but erasable). Note that only backup instances are readonly, because other trace instances will be empty unless it is writable. Only backup instances have copy entries from the original. With this change, most of the trace control files are removed from the backup instance, including eventfs enable/filter etc. # find /sys/kernel/tracing/instances/backup/events/ | wc -l 4093 # find /sys/kernel/tracing/instances/boot_map/events/ | wc -l 9573 Signed-off-by: Masami Hiramatsu (Google) --- Changes in v6: - Remove tracing_on file from readonly instances. - Remove unused writable_mode from tracing_init_tracefs_percpu(). - Cleanup init_tracer_tracefs() and create_event_toplevel_files(). - Remove TRACE_MODE_WRITE_MASK. - Add TRACE_ARRAY_FL_RDONLY. Changes in v5: - Rebased on the latest for-next (and hide show_event_filters/triggers if the instance is readonly. Changes in v4: - Make trace data erasable. (not reusable) Changes in v3: - Resuse the beginning part of event_entries for readonly files. - Remove readonly file_operations and checking readonly flag in each write operation. Changes in v2: - Use readonly file_operations to prohibit writing instead of checking flags in write() callbacks. - Remove writable files from eventfs. --- kernel/trace/trace.c | 94 +++++++++++++++++++++++++++++----------= ---- kernel/trace/trace.h | 7 +++ kernel/trace/trace_boot.c | 5 +- kernel/trace/trace_events.c | 76 ++++++++++++++++++++--------------- 4 files changed, 117 insertions(+), 65 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 5c3e4a554143..b0efcf1e0809 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5052,6 +5052,11 @@ static ssize_t tracing_write_stub(struct file *filp, const char __user *ubuf, size_t count, loff_t *ppos) { + struct trace_array *tr =3D file_inode(filp)->i_private; + + if (trace_array_is_readonly(tr)) + return -EPERM; + return count; } =20 @@ -5152,6 +5157,9 @@ tracing_cpumask_write(struct file *filp, const char _= _user *ubuf, cpumask_var_t tracing_cpumask_new; int err; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + if (count =3D=3D 0 || count > KMALLOC_MAX_SIZE) return -EINVAL; =20 @@ -6436,6 +6444,9 @@ tracing_set_trace_write(struct file *filp, const char= __user *ubuf, size_t ret; int err; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + ret =3D cnt; =20 if (cnt > MAX_TRACER_SIZE) @@ -7070,6 +7081,9 @@ tracing_entries_write(struct file *filp, const char _= _user *ubuf, unsigned long val; int ret; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + ret =3D kstrtoul_from_user(ubuf, cnt, 10, &val); if (ret) return ret; @@ -7824,6 +7838,9 @@ static ssize_t tracing_clock_write(struct file *filp,= const char __user *ubuf, const char *clockstr; int ret; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + if (cnt >=3D sizeof(buf)) return -EINVAL; =20 @@ -9846,6 +9863,9 @@ rb_simple_write(struct file *filp, const char __user = *ubuf, unsigned long val; int ret; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + ret =3D kstrtoul_from_user(ubuf, cnt, 10, &val); if (ret) return ret; @@ -9952,6 +9972,9 @@ buffer_subbuf_size_write(struct file *filp, const cha= r __user *ubuf, int pages; int ret; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + ret =3D kstrtoul_from_user(ubuf, cnt, 10, &val); if (ret) return ret; @@ -10632,17 +10655,22 @@ static __init void create_trace_instances(struct = dentry *d_tracer) static void init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer) { + umode_t writable_mode =3D TRACE_MODE_WRITE; int cpu; =20 + if (trace_array_is_readonly(tr)) + writable_mode =3D TRACE_MODE_READ; + trace_create_file("available_tracers", TRACE_MODE_READ, d_tracer, - tr, &show_traces_fops); + tr, &show_traces_fops); =20 - trace_create_file("current_tracer", TRACE_MODE_WRITE, d_tracer, - tr, &set_tracer_fops); + trace_create_file("current_tracer", writable_mode, d_tracer, + tr, &set_tracer_fops); =20 - trace_create_file("tracing_cpumask", TRACE_MODE_WRITE, d_tracer, + trace_create_file("tracing_cpumask", writable_mode, d_tracer, tr, &tracing_cpumask_fops); =20 + /* Options are used for changing print-format even for readonly instance.= */ trace_create_file("trace_options", TRACE_MODE_WRITE, d_tracer, tr, &tracing_iter_fops); =20 @@ -10652,12 +10680,36 @@ init_tracer_tracefs(struct trace_array *tr, struc= t dentry *d_tracer) trace_create_file("trace_pipe", TRACE_MODE_READ, d_tracer, tr, &tracing_pipe_fops); =20 - trace_create_file("buffer_size_kb", TRACE_MODE_WRITE, d_tracer, + trace_create_file("buffer_size_kb", writable_mode, d_tracer, tr, &tracing_entries_fops); =20 trace_create_file("buffer_total_size_kb", TRACE_MODE_READ, d_tracer, tr, &tracing_total_entries_fops); =20 + trace_create_file("trace_clock", writable_mode, d_tracer, tr, + &trace_clock_fops); + + trace_create_file("timestamp_mode", TRACE_MODE_READ, d_tracer, tr, + &trace_time_stamp_mode_fops); + + tr->buffer_percent =3D 50; + + trace_create_file("buffer_subbuf_size_kb", writable_mode, d_tracer, + tr, &buffer_subbuf_size_fops); + + create_trace_options_dir(tr); + + if (tr->range_addr_start) + trace_create_file("last_boot_info", TRACE_MODE_READ, d_tracer, + tr, &last_boot_fops); + + for_each_tracing_cpu(cpu) + tracing_init_tracefs_percpu(tr, cpu); + + /* Read-only instance has above files only. */ + if (trace_array_is_readonly(tr)) + return; + trace_create_file("free_buffer", 0200, d_tracer, tr, &tracing_free_buffer_fops); =20 @@ -10669,27 +10721,14 @@ init_tracer_tracefs(struct trace_array *tr, struc= t dentry *d_tracer) trace_create_file("trace_marker_raw", 0220, d_tracer, tr, &tracing_mark_raw_fops); =20 - trace_create_file("trace_clock", TRACE_MODE_WRITE, d_tracer, tr, - &trace_clock_fops); - - trace_create_file("tracing_on", TRACE_MODE_WRITE, d_tracer, - tr, &rb_simple_fops); - - trace_create_file("timestamp_mode", TRACE_MODE_READ, d_tracer, tr, - &trace_time_stamp_mode_fops); - - tr->buffer_percent =3D 50; - trace_create_file("buffer_percent", TRACE_MODE_WRITE, d_tracer, - tr, &buffer_percent_fops); - - trace_create_file("buffer_subbuf_size_kb", TRACE_MODE_WRITE, d_tracer, - tr, &buffer_subbuf_size_fops); + tr, &buffer_percent_fops); =20 trace_create_file("syscall_user_buf_size", TRACE_MODE_WRITE, d_tracer, - tr, &tracing_syscall_buf_fops); + tr, &tracing_syscall_buf_fops); =20 - create_trace_options_dir(tr); + trace_create_file("tracing_on", TRACE_MODE_WRITE, d_tracer, + tr, &rb_simple_fops); =20 #ifdef CONFIG_TRACER_MAX_TRACE trace_create_maxlat_file(tr, d_tracer); @@ -10698,22 +10737,15 @@ init_tracer_tracefs(struct trace_array *tr, struc= t dentry *d_tracer) if (ftrace_create_function_files(tr, d_tracer)) MEM_FAIL(1, "Could not allocate function filter files"); =20 - if (tr->range_addr_start) { - trace_create_file("last_boot_info", TRACE_MODE_READ, d_tracer, - tr, &last_boot_fops); #ifdef CONFIG_TRACER_SNAPSHOT - } else { + if (!tr->range_addr_start) trace_create_file("snapshot", TRACE_MODE_WRITE, d_tracer, tr, &snapshot_fops); #endif - } =20 trace_create_file("error_log", TRACE_MODE_WRITE, d_tracer, tr, &tracing_err_log_fops); =20 - for_each_tracing_cpu(cpu) - tracing_init_tracefs_percpu(tr, cpu); - ftrace_init_tracefs(tr, d_tracer); } =20 @@ -11540,7 +11572,7 @@ __init static void enable_instances(void) * Backup buffers can be freed but need vfree(). */ if (backup) - tr->flags |=3D TRACE_ARRAY_FL_VMALLOC; + tr->flags |=3D TRACE_ARRAY_FL_VMALLOC | TRACE_ARRAY_FL_RDONLY; =20 if (start || backup) { tr->flags |=3D TRACE_ARRAY_FL_BOOT | TRACE_ARRAY_FL_LAST_BOOT; diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 69e7defba6c6..4ff7ebd8a32b 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -455,6 +455,7 @@ enum { TRACE_ARRAY_FL_MOD_INIT =3D BIT(3), TRACE_ARRAY_FL_MEMMAP =3D BIT(4), TRACE_ARRAY_FL_VMALLOC =3D BIT(5), + TRACE_ARRAY_FL_RDONLY =3D BIT(6), }; =20 #ifdef CONFIG_MODULES @@ -483,6 +484,12 @@ extern bool trace_clock_in_ns(struct trace_array *tr); =20 extern unsigned long trace_adjust_address(struct trace_array *tr, unsigned= long addr); =20 +static inline bool trace_array_is_readonly(struct trace_array *tr) +{ + /* backup instance is read only. */ + return tr->flags & TRACE_ARRAY_FL_RDONLY; +} + /* * The global tracer (top) should be the first trace array added, * but we check the flag anyway. diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c index dbe29b4c6a7a..2ca2541c8a58 100644 --- a/kernel/trace/trace_boot.c +++ b/kernel/trace/trace_boot.c @@ -61,7 +61,8 @@ trace_boot_set_instance_options(struct trace_array *tr, s= truct xbc_node *node) v =3D memparse(p, NULL); if (v < PAGE_SIZE) pr_err("Buffer size is too small: %s\n", p); - if (tracing_resize_ring_buffer(tr, v, RING_BUFFER_ALL_CPUS) < 0) + if (trace_array_is_readonly(tr) || + tracing_resize_ring_buffer(tr, v, RING_BUFFER_ALL_CPUS) < 0) pr_err("Failed to resize trace buffer to %s\n", p); } =20 @@ -597,7 +598,7 @@ trace_boot_enable_tracer(struct trace_array *tr, struct= xbc_node *node) =20 p =3D xbc_node_find_value(node, "tracer", NULL); if (p && *p !=3D '\0') { - if (tracing_set_tracer(tr, p) < 0) + if (trace_array_is_readonly(tr) || tracing_set_tracer(tr, p) < 0) pr_err("Failed to set given tracer: %s\n", p); } =20 diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 4972e1a2b5f3..16b9f222407c 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1380,6 +1380,9 @@ static int __ftrace_set_clr_event(struct trace_array = *tr, const char *match, { int ret; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + mutex_lock(&event_mutex); ret =3D __ftrace_set_clr_event_nolock(tr, match, sub, event, set, mod); mutex_unlock(&event_mutex); @@ -2952,8 +2955,8 @@ event_subsystem_dir(struct trace_array *tr, const cha= r *name, } else __get_system(system); =20 - /* ftrace only has directories no files */ - if (strcmp(name, "ftrace") =3D=3D 0) + /* ftrace only has directories no files, readonly instance too. */ + if (strcmp(name, "ftrace") =3D=3D 0 || trace_array_is_readonly(tr)) nr_entries =3D 0; else nr_entries =3D ARRAY_SIZE(system_entries); @@ -3118,28 +3121,30 @@ event_create_dir(struct eventfs_inode *parent, stru= ct trace_event_file *file) int ret; static struct eventfs_entry event_entries[] =3D { { - .name =3D "enable", + .name =3D "format", .callback =3D event_callback, - .release =3D event_release, }, +#ifdef CONFIG_PERF_EVENTS { - .name =3D "filter", + .name =3D "id", .callback =3D event_callback, }, +#endif +#define NR_RO_EVENT_ENTRIES (1 + IS_ENABLED(CONFIG_PERF_EVENTS)) +/* Readonly files must be above this line and counted by NR_RO_EVENT_ENTRI= ES. */ { - .name =3D "trigger", + .name =3D "enable", .callback =3D event_callback, + .release =3D event_release, }, { - .name =3D "format", + .name =3D "filter", .callback =3D event_callback, }, -#ifdef CONFIG_PERF_EVENTS { - .name =3D "id", + .name =3D "trigger", .callback =3D event_callback, }, -#endif #ifdef CONFIG_HIST_TRIGGERS { .name =3D "hist", @@ -3172,7 +3177,10 @@ event_create_dir(struct eventfs_inode *parent, struc= t trace_event_file *file) if (!e_events) return -ENOMEM; =20 - nr_entries =3D ARRAY_SIZE(event_entries); + if (trace_array_is_readonly(tr)) + nr_entries =3D NR_RO_EVENT_ENTRIES; + else + nr_entries =3D ARRAY_SIZE(event_entries); =20 name =3D trace_event_name(call); ei =3D eventfs_create_dir(name, e_events, event_entries, nr_entries, file= ); @@ -4511,31 +4519,44 @@ create_event_toplevel_files(struct dentry *parent, = struct trace_array *tr) int nr_entries; static struct eventfs_entry events_entries[] =3D { { - .name =3D "enable", + .name =3D "header_page", .callback =3D events_callback, }, { - .name =3D "header_page", + .name =3D "header_event", .callback =3D events_callback, }, +#define NR_RO_TOP_ENTRIES 2 +/* Readonly files must be above this line and counted by NR_RO_TOP_ENTRIES= . */ { - .name =3D "header_event", + .name =3D "enable", .callback =3D events_callback, }, }; =20 - entry =3D trace_create_file("set_event", TRACE_MODE_WRITE, parent, - tr, &ftrace_set_event_fops); - if (!entry) - return -ENOMEM; + if (!trace_array_is_readonly(tr)) { + entry =3D trace_create_file("set_event", TRACE_MODE_WRITE, parent, + tr, &ftrace_set_event_fops); + if (!entry) + return -ENOMEM; =20 - trace_create_file("show_event_filters", TRACE_MODE_READ, parent, tr, - &ftrace_show_event_filters_fops); + /* There are not as crucial, just warn if they are not created */ + trace_create_file("show_event_filters", TRACE_MODE_READ, parent, tr, + &ftrace_show_event_filters_fops); =20 - trace_create_file("show_event_triggers", TRACE_MODE_READ, parent, tr, - &ftrace_show_event_triggers_fops); + trace_create_file("show_event_triggers", TRACE_MODE_READ, parent, tr, + &ftrace_show_event_triggers_fops); =20 - nr_entries =3D ARRAY_SIZE(events_entries); + trace_create_file("set_event_pid", TRACE_MODE_WRITE, parent, + tr, &ftrace_set_event_pid_fops); + + trace_create_file("set_event_notrace_pid", + TRACE_MODE_WRITE, parent, tr, + &ftrace_set_event_notrace_pid_fops); + nr_entries =3D ARRAY_SIZE(events_entries); + } else { + nr_entries =3D NR_RO_TOP_ENTRIES; + } =20 e_events =3D eventfs_create_events_dir("events", parent, events_entries, nr_entries, tr); @@ -4544,15 +4565,6 @@ create_event_toplevel_files(struct dentry *parent, s= truct trace_array *tr) return -ENOMEM; } =20 - /* There are not as crucial, just warn if they are not created */ - - trace_create_file("set_event_pid", TRACE_MODE_WRITE, parent, - tr, &ftrace_set_event_pid_fops); - - trace_create_file("set_event_notrace_pid", - TRACE_MODE_WRITE, parent, tr, - &ftrace_set_event_notrace_pid_fops); - tr->event_dir =3D e_events; =20 return 0; From nobody Mon Feb 9 11:34:03 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 03004274B59; Sun, 1 Feb 2026 03:29:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769916565; cv=none; b=tShcPh++VYlfeugBZo3oCnJYMHkyTOoyrN2jUnUisVQrTa83G2wt4iBUSz09RwI8e11fIu1eTplZryr2AtfJI9g0qDUhx3nRgE7s0fa5U1u3glQ3doomg12BjMvxKdfFPmYzheWVH8FAvEf0qEet/9i9BJxyECi4cbnvNlWv1Po= ARC-Message-Signature: i=1; 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b=t2RGyOeF3TDVaGsY924oPHfHb0OizKRutecHXWztOdw0yY1RWXEOSQ6roFzgPxsrz Ws2b2b6BZQGSbJhf7aIvSGE1yDBBkajngcYvCGzdNvXvCYz2inmn2ZngKpcoyFt5mr uv+Oe/0pcUL9t5thsFZXTVyhydGzcojJ2XVe6iE17/Fyw2SiyRuY6zNRiHkyffgcwP LolSc3CquJqMNcSkFGzgA05kdowpPpVYVkCz6qff5dyTJcNWkhpBCTt9pgejWIRDwg KCTI6aFfUWf6u9C2g7h9WhYKYzYNYKk++HkfvnzGOonnFORjt9edP0nxrkrz5pBi3F /s3F+pNjdch7A== From: "Masami Hiramatsu (Google)" To: Steven Rostedt Cc: Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: [PATCH v6 3/4] tracing: Remove the backup instance automatically after read Date: Sun, 1 Feb 2026 12:29:22 +0900 Message-ID: <176991656245.4025429.16456388648872177605.stgit@mhiramat.tok.corp.google.com> X-Mailer: git-send-email 2.53.0.rc1.225.gd81095ad13-goog In-Reply-To: <176991653525.4025429.12655335935351822711.stgit@mhiramat.tok.corp.google.com> References: <176991653525.4025429.12655335935351822711.stgit@mhiramat.tok.corp.google.com> User-Agent: StGit/0.19 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" Content-Transfer-Encoding: quoted-printable From: Masami Hiramatsu (Google) Since the backup instance is readonly, after reading all data via pipe, no data is left on the instance. Thus it can be removed safely after closing all files. This also removes it if user resets the ring buffer manually via 'trace' file. Signed-off-by: Masami Hiramatsu (Google) --- Changes in v6: - Fix typo in comment. - Only when there is a readonly trace array, initialize autoremove_wq. - Fix to exit loop in trace_array_get() if tr is found in the list. Changes in v4: - Update description. --- kernel/trace/trace.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++= +++- kernel/trace/trace.h | 6 +++++ 2 files changed, 66 insertions(+), 1 deletion(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index b0efcf1e0809..9d09befd5da5 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -590,6 +590,51 @@ void trace_set_ring_buffer_expanded(struct trace_array= *tr) tr->ring_buffer_expanded =3D true; } =20 +static int __remove_instance(struct trace_array *tr); + +static void trace_array_autoremove(struct work_struct *work) +{ + struct trace_array *tr =3D container_of(work, struct trace_array, autorem= ove_work); + + guard(mutex)(&event_mutex); + guard(mutex)(&trace_types_lock); + + /* + * This can be fail if someone gets @tr before starting this + * function, but in that case, this will be kicked again when + * putting it. So we don't care about the result. + */ + __remove_instance(tr); +} + +static struct workqueue_struct *autoremove_wq; + +static void trace_array_kick_autoremove(struct trace_array *tr) +{ + if (autoremove_wq && !work_pending(&tr->autoremove_work)) + queue_work(autoremove_wq, &tr->autoremove_work); +} + +static void trace_array_cancel_autoremove(struct trace_array *tr) +{ + if (autoremove_wq && work_pending(&tr->autoremove_work)) + cancel_work(&tr->autoremove_work); +} + +static void trace_array_init_autoremove(struct trace_array *tr) +{ + INIT_WORK(&tr->autoremove_work, trace_array_autoremove); + + /* Only readonly trace_array can kick the autoremove. */ + if (!trace_array_is_readonly(tr) || autoremove_wq) + return; + + autoremove_wq =3D alloc_workqueue("tr_autoremove_wq", + WQ_UNBOUND | WQ_HIGHPRI, 0); + if (!autoremove_wq) + pr_warn("Unable to allocate tr_autoremove_wq. autoremove disabled.\n"); +} + LIST_HEAD(ftrace_trace_arrays); =20 int trace_array_get(struct trace_array *this_tr) @@ -599,7 +644,8 @@ int trace_array_get(struct trace_array *this_tr) guard(mutex)(&trace_types_lock); list_for_each_entry(tr, &ftrace_trace_arrays, list) { if (tr =3D=3D this_tr) { - tr->ref++; + if (!tr->free_on_close) + tr->ref++; return 0; } } @@ -611,6 +657,12 @@ static void __trace_array_put(struct trace_array *this= _tr) { WARN_ON(!this_tr->ref); this_tr->ref--; + /* + * When free_on_close is set, prepare removing the array + * when the last reference is released. + */ + if (this_tr->ref =3D=3D 1 && this_tr->free_on_close) + trace_array_kick_autoremove(this_tr); } =20 /** @@ -6237,6 +6289,10 @@ static void update_last_data(struct trace_array *tr) /* Only if the buffer has previous boot data clear and update it. */ tr->flags &=3D ~TRACE_ARRAY_FL_LAST_BOOT; =20 + /* If this is a backup instance, mark it for autoremove. */ + if (tr->flags & TRACE_ARRAY_FL_VMALLOC) + tr->free_on_close =3D true; + /* Reset the module list and reload them */ if (tr->scratch) { struct trace_scratch *tscratch =3D tr->scratch; @@ -10415,6 +10471,8 @@ trace_array_create_systems(const char *name, const = char *systems, if (ftrace_allocate_ftrace_ops(tr) < 0) goto out_free_tr; =20 + trace_array_init_autoremove(tr); + ftrace_init_trace_array(tr); =20 init_trace_flags_index(tr); @@ -10563,6 +10621,7 @@ static int __remove_instance(struct trace_array *tr) if (update_marker_trace(tr, 0)) synchronize_rcu(); =20 + trace_array_cancel_autoremove(tr); tracing_set_nop(tr); clear_ftrace_function_probes(tr); event_trace_del_tracer(tr); diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 4ff7ebd8a32b..4c5ef9d8f8ad 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -446,6 +446,12 @@ struct trace_array { * we do not waste memory on systems that are not using tracing. */ bool ring_buffer_expanded; + /* + * If the ring buffer is a read only backup instance, it will be + * removed after dumping all data via pipe, because no readable data. + */ + bool free_on_close; + struct work_struct autoremove_work; }; =20 enum { From nobody Mon Feb 9 11:34:03 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 F3F3D274B59; 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dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="K8882s9/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D0942C4CEF7; Sun, 1 Feb 2026 03:29:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769916572; bh=S5HUOKOwvhSR3nZmMfKa96wdR+Qt2kEIy+bpCsLdFdo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=K8882s9/3Kfdc2IlteSXUjy/vV33PZkt3pEOqFMHaeAA/5ZsXNcq7enW1/gxJbDHK gCT9/RHmK3+678+YbK2VHyCnJXz1QR9m5m3FBenjVW0ks4oaJ12hDEoiw/+FsHCDuQ yYU3fEuPNEroRl99G8DbV7aiLJE38o45GGo2Gmr1KviF7FwqTTXQR/VMmO2AfEtPo8 lsdP1A5XxBTeY//qHPl/r8s3Al7aeDLQXxYn7PbungV1voCLieKSlFw0Ir26yvO3YT +yKvuI57+uQOQ9LcnHQhvs2pmUc2faq9CQP4YAITq+DCdzxjS6woEgWOemwgzENp6s zn61HZ7FSm/6w== From: "Masami Hiramatsu (Google)" To: Steven Rostedt Cc: Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: [PATCH v6 4/4] tracing/Documentation: Add a section about backup instance Date: Sun, 1 Feb 2026 12:29:30 +0900 Message-ID: <176991657015.4025429.14835098082961554583.stgit@mhiramat.tok.corp.google.com> X-Mailer: git-send-email 2.53.0.rc1.225.gd81095ad13-goog In-Reply-To: <176991653525.4025429.12655335935351822711.stgit@mhiramat.tok.corp.google.com> References: <176991653525.4025429.12655335935351822711.stgit@mhiramat.tok.corp.google.com> User-Agent: StGit/0.19 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" Content-Transfer-Encoding: quoted-printable From: Masami Hiramatsu (Google) Add a section about backup instance to the debugging.rst. Signed-off-by: Masami Hiramatsu (Google) --- Changes in v6: - Fix typos. --- Documentation/trace/debugging.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/trace/debugging.rst b/Documentation/trace/debugg= ing.rst index 4d88c346fc38..15857951b506 100644 --- a/Documentation/trace/debugging.rst +++ b/Documentation/trace/debugging.rst @@ -159,3 +159,22 @@ If setting it from the kernel command line, it is reco= mmended to also disable tracing with the "traceoff" flag, and enable tracing after boot up. Otherwise the trace from the most recent boot will be mixed with the trace from the previous boot, and may make it confusing to read. + +Using a backup instance for keeping previous boot data +------------------------------------------------------ + +It is also possible to record trace data at system boot time by specifying +events with the persistent ring buffer, but in this case the data before t= he +reboot will be lost before it can be read. This problem can be solved by a +backup instance. From the kernel command line:: + + reserve_mem=3D12M:4096:trace trace_instance=3Dboot_map@trace,sched,irq t= race_instance=3Dbackup=3Dboot_map + +On boot up, the previous data in the "boot_map" is copied to the "backup" +instance, and the "sched:*" and "irq:*" events for the current boot are tr= aced +in the "boot_map". Thus the user can read the previous boot data from the = "backup" +instance without stopping the trace. + +Note that this "backup" instance is readonly, and will be removed automati= cally +if you clear the trace data or read out all trace data from the "trace_pip= e" +or the "trace_pipe_raw" files. \ No newline at end of file