From nobody Mon Feb 9 23:40:17 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 436BC329E50; Wed, 7 Jan 2026 14:46:01 +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=1767797162; cv=none; b=OkUPMkUzI6NG7oU0m0TR65nJZBUJXhZm+YQWscNlJ56xrlS63AiD0cINJBb/tiaYkjRhwVN18O8OHuoX3PmkMEIIQp6Ohw1UnMxnEbyOik9jcCX9zx+yoSlWVp/LdQyIS7arzmBdHpEuiimhQxnb0y+Kh3r5bKNhdigkC/ay4XY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767797162; c=relaxed/simple; bh=ILQXUKNpEe3BjjH3CX4Ik/HEyu15DTzkgyeIBNzl8ig=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=gvtP36HCMAWues0gjgmJnNJaCwWb1WE/fAsIfTmiIkO6dhvo0ZpGJsMddclwCZlB0574gNe2uZFNOhCeQ8CEOwIwZ+ZuBWUXkC7u5QglESWZ1ruIHuvCC4SofIUEFn4rFZenZMEj0ZSy+Vrjl0dybveYgCs38pa0dOHpjAQiEUo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SMG1kumJ; 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="SMG1kumJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1734DC4CEF1; Wed, 7 Jan 2026 14:46:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767797161; bh=ILQXUKNpEe3BjjH3CX4Ik/HEyu15DTzkgyeIBNzl8ig=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SMG1kumJc6yi9KXy7/1xJY4Br5gQerjaOyam1LfbWvRJ0mlTQ+7jJVxmuDpbQtN/f vjlgh7IHvL8pjXCPtq9C6emliTSunzFr0T2bcDqNhszloGCNOcNCCJqQz1uJvJ88V2 XQ3ThtD9150Yvf0TJd502YnAO5xGblkcXM8D8XkA2HryfZPyVGzz6Eh6BSfb+JNMSw v+oC1LZm4vYvQfM0zcG2JIxTcLdrSTL/XTqlkNlaTk9ijNV9ZujUgbsfMbG+JzCKZv BhfL0q1F5SX3JhRXGMWmHsdERy6C+erPzKH57U5E+ptyj9oESyWffk5t7YDsEEuRzB XtzVlb+d9Zeyg== 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 1/2] tracing: Make the backup instance readonly Date: Wed, 7 Jan 2026 23:45:59 +0900 Message-ID: <176779715937.4193242.8486149802702305279.stgit@mhiramat.tok.corp.google.com> X-Mailer: git-send-email 2.52.0.351.gbe84eed79e-goog In-Reply-To: <176779714767.4193242.1978666866487010024.stgit@mhiramat.tok.corp.google.com> References: <176779714767.4193242.1978666866487010024.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. 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. Signed-off-by: Masami Hiramatsu (Google) --- kernel/trace/trace.c | 91 ++++++++++++++++++++++++++++++++-------= ---- kernel/trace/trace.h | 6 +++ kernel/trace/trace_events.c | 14 +++++-- 3 files changed, 84 insertions(+), 27 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 38f7a7a55c23..725930f5980e 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4888,6 +4888,9 @@ static int tracing_open(struct inode *inode, struct f= ile *file) int cpu =3D tracing_get_cpu(inode); struct array_buffer *trace_buf =3D &tr->array_buffer; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + #ifdef CONFIG_TRACER_MAX_TRACE if (tr->current_trace->print_max) trace_buf =3D &tr->max_buffer; @@ -6077,6 +6080,9 @@ static int __tracing_resize_ring_buffer(struct trace_= array *tr, ssize_t tracing_resize_ring_buffer(struct trace_array *tr, unsigned long size, int cpu_id) { + if (trace_array_is_readonly(tr)) + return -EPERM; + guard(mutex)(&trace_types_lock); =20 if (cpu_id !=3D RING_BUFFER_ALL_CPUS) { @@ -6298,6 +6304,10 @@ int tracing_set_tracer(struct trace_array *tr, const= char *buf) =20 guard(mutex)(&trace_types_lock); =20 + /* Not allowed to set new tracer on readonly instance. */ + if (trace_array_is_readonly(tr)) + return -EPERM; + update_last_data(tr); =20 if (!tr->ring_buffer_expanded) { @@ -6413,6 +6423,9 @@ 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) @@ -6478,6 +6491,9 @@ tracing_thresh_write(struct file *filp, const char __= user *ubuf, struct trace_array *tr =3D filp->private_data; int ret; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + guard(mutex)(&trace_types_lock); ret =3D tracing_nsecs_write(&tracing_thresh, ubuf, cnt, ppos); if (ret < 0) @@ -7047,6 +7063,9 @@ 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; @@ -7595,6 +7614,9 @@ tracing_mark_write(struct file *filp, const char __us= er *ubuf, unsigned long ip; char *buf; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + if (tracing_disabled) return -EINVAL; =20 @@ -7675,6 +7697,9 @@ tracing_mark_raw_write(struct file *filp, const char = __user *ubuf, ssize_t written =3D -ENODEV; char *buf; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + if (tracing_disabled) return -EINVAL; =20 @@ -7757,6 +7782,9 @@ int tracing_set_clock(struct trace_array *tr, const c= har *clockstr) { int i; =20 + if (trace_array_is_readonly(tr)) + return -EPERM; + for (i =3D 0; i < ARRAY_SIZE(trace_clocks); i++) { if (strcmp(trace_clocks[i].name, clockstr) =3D=3D 0) break; @@ -9353,12 +9381,16 @@ static void tracing_init_tracefs_percpu(struct trace_array *tr, long cpu) { struct dentry *d_percpu =3D tracing_dentry_percpu(tr, cpu); + umode_t writable_mode =3D TRACE_MODE_WRITE; struct dentry *d_cpu; char cpu_dir[30]; /* 30 characters should be more than enough */ =20 if (!d_percpu) return; =20 + if (trace_array_is_readonly(tr)) + writable_mode =3D TRACE_MODE_READ; + snprintf(cpu_dir, 30, "cpu%ld", cpu); d_cpu =3D tracefs_create_dir(cpu_dir, d_percpu); if (!d_cpu) { @@ -9371,7 +9403,7 @@ tracing_init_tracefs_percpu(struct trace_array *tr, l= ong cpu) tr, cpu, &tracing_pipe_fops); =20 /* per cpu trace */ - trace_create_cpu_file("trace", TRACE_MODE_WRITE, d_cpu, + trace_create_cpu_file("trace", writable_mode, d_cpu, tr, cpu, &tracing_fops); =20 trace_create_cpu_file("trace_pipe_raw", TRACE_MODE_READ, d_cpu, @@ -9811,6 +9843,9 @@ 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; @@ -10597,47 +10632,54 @@ 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; + bool readonly =3D trace_array_is_readonly(tr); int cpu; =20 + if (readonly) + writable_mode =3D TRACE_MODE_READ; + trace_create_file("available_tracers", TRACE_MODE_READ, d_tracer, tr, &show_traces_fops); =20 - trace_create_file("current_tracer", TRACE_MODE_WRITE, d_tracer, + 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 - trace_create_file("trace_options", TRACE_MODE_WRITE, d_tracer, + trace_create_file("trace_options", writable_mode, d_tracer, tr, &tracing_iter_fops); =20 - trace_create_file("trace", TRACE_MODE_WRITE, d_tracer, + trace_create_file("trace", writable_mode, d_tracer, tr, &tracing_fops); =20 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("free_buffer", 0200, d_tracer, - tr, &tracing_free_buffer_fops); + if (!readonly) { + trace_create_file("free_buffer", 0200, d_tracer, + tr, &tracing_free_buffer_fops); =20 - trace_create_file("trace_marker", 0220, d_tracer, - tr, &tracing_mark_fops); + trace_create_file("trace_marker", 0220, d_tracer, + tr, &tracing_mark_fops); =20 - tr->trace_marker_file =3D __find_event_file(tr, "ftrace", "print"); + tr->trace_marker_file =3D __find_event_file(tr, "ftrace", "print"); =20 - trace_create_file("trace_marker_raw", 0220, d_tracer, - tr, &tracing_mark_raw_fops); + 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_create_file("trace_clock", writable_mode, d_tracer, tr, &trace_clock_fops); =20 - trace_create_file("tracing_on", TRACE_MODE_WRITE, d_tracer, + trace_create_file("tracing_on", writable_mode, d_tracer, tr, &rb_simple_fops); =20 trace_create_file("timestamp_mode", TRACE_MODE_READ, d_tracer, tr, @@ -10645,22 +10687,23 @@ init_tracer_tracefs(struct trace_array *tr, struc= t dentry *d_tracer) =20 tr->buffer_percent =3D 50; =20 - trace_create_file("buffer_percent", TRACE_MODE_WRITE, d_tracer, + trace_create_file("buffer_percent", writable_mode, d_tracer, tr, &buffer_percent_fops); =20 - trace_create_file("buffer_subbuf_size_kb", TRACE_MODE_WRITE, d_tracer, + trace_create_file("buffer_subbuf_size_kb", writable_mode, d_tracer, tr, &buffer_subbuf_size_fops); =20 - trace_create_file("syscall_user_buf_size", TRACE_MODE_WRITE, d_tracer, + trace_create_file("syscall_user_buf_size", writable_mode, d_tracer, tr, &tracing_syscall_buf_fops); =20 create_trace_options_dir(tr); =20 #ifdef CONFIG_TRACER_MAX_TRACE - trace_create_maxlat_file(tr, d_tracer); + if (!readonly) + trace_create_maxlat_file(tr, d_tracer); #endif =20 - if (ftrace_create_function_files(tr, d_tracer)) + if (!readonly && ftrace_create_function_files(tr, d_tracer)) MEM_FAIL(1, "Could not allocate function filter files"); =20 if (tr->range_addr_start) { @@ -10673,13 +10716,15 @@ init_tracer_tracefs(struct trace_array *tr, struc= t dentry *d_tracer) #endif } =20 - trace_create_file("error_log", TRACE_MODE_WRITE, d_tracer, - tr, &tracing_err_log_fops); + if (!readonly) + 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); =20 - ftrace_init_tracefs(tr, d_tracer); + if (!readonly) + ftrace_init_tracefs(tr, d_tracer); } =20 #ifdef CONFIG_TRACEFS_AUTOMOUNT_DEPRECATED diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index b6d42fe06115..bc0eeb2d1d07 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -483,6 +483,12 @@ 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_VMALLOC; +} + /* * The global tracer (top) should be the first trace array added, * but we check the flag anyway. diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 9b07ad9eb284..f20f717f1ea9 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1379,6 +1379,9 @@ 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); @@ -4376,6 +4379,7 @@ static int events_callback(const char *name, umode_t = *mode, void **data, static int create_event_toplevel_files(struct dentry *parent, struct trace_array *tr) { + umode_t writable_mode =3D TRACE_MODE_WRITE; struct eventfs_inode *e_events; struct dentry *entry; int nr_entries; @@ -4393,9 +4397,11 @@ create_event_toplevel_files(struct dentry *parent, s= truct trace_array *tr) .callback =3D events_callback, }, }; + if (trace_array_is_readonly(tr)) + writable_mode =3D TRACE_MODE_READ; =20 - entry =3D trace_create_file("set_event", TRACE_MODE_WRITE, parent, - tr, &ftrace_set_event_fops); + entry =3D trace_create_file("set_event", writable_mode, parent, + tr, &ftrace_set_event_fops); if (!entry) return -ENOMEM; =20 @@ -4410,11 +4416,11 @@ create_event_toplevel_files(struct dentry *parent, = struct trace_array *tr) =20 /* There are not as crucial, just warn if they are not created */ =20 - trace_create_file("set_event_pid", TRACE_MODE_WRITE, parent, + trace_create_file("set_event_pid", writable_mode, parent, tr, &ftrace_set_event_pid_fops); =20 trace_create_file("set_event_notrace_pid", - TRACE_MODE_WRITE, parent, tr, + writable_mode, parent, tr, &ftrace_set_event_notrace_pid_fops); =20 tr->event_dir =3D e_events;