* [PATCH v4 0/4] tracing: Remove backup instance after read all
@ 2026-01-20 1:09 Masami Hiramatsu (Google)
2026-01-20 1:09 ` [PATCH v4 1/4] tracing: Reset last_boot_info if ring buffer is reset Masami Hiramatsu (Google)
` (3 more replies)
0 siblings, 4 replies; 6+ messages in thread
From: Masami Hiramatsu (Google) @ 2026-01-20 1:09 UTC (permalink / raw)
To: Steven Rostedt
Cc: Masami Hiramatsu, Mathieu Desnoyers, linux-kernel,
linux-trace-kernel
Hi,
Here is the 4th version of the series to improve backup instances of
the persistent ring buffer. The previous version is here:
https://lore.kernel.org/all/176828713313.2161268.62228177827727824.stgit@mhiramat.tok.corp.google.com/
In this version, I added new fix [1/4] to reset last_boot_info when
the ring buffer is reset. [2/4] is updated to allow resetting the
readonly ring buffer via trace file. And [4/4] is adding a section
for the backup instance to `debugging.rst`.
Since backup instances are a kind of snapshot of the persistent
ring buffer, it should be readonly. And if it is readonly
there is no reason to keep it after reading all data via trace_pipe
because the data has been consumed. But user should be able to remove
the readonly instance by rmdir or truncating `trace` file.
Thus, [2/3] makes backup instances readonly (not able to write any
events, cleanup trace, change buffer size). Also, [3/3] removes the
backup instance after consuming all data via trace_pipe.
With this improvements, even if we makes a backup instance (using
the same amount of memory of the persistent ring buffer), it will
be removed after reading the data automatically.
---
Masami Hiramatsu (Google) (4):
tracing: Reset last_boot_info if ring buffer is reset
tracing: Make the backup instance non-reusable
tracing: Remove the backup instance automatically after read
tracing/Documentation: Add a section about backup instance
Documentation/trace/debugging.rst | 19 ++++
kernel/trace/trace.c | 164 ++++++++++++++++++++++++++++++-------
kernel/trace/trace.h | 14 +++
kernel/trace/trace_boot.c | 5 +
kernel/trace/trace_events.c | 68 +++++++++------
5 files changed, 212 insertions(+), 58 deletions(-)
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH v4 1/4] tracing: Reset last_boot_info if ring buffer is reset 2026-01-20 1:09 [PATCH v4 0/4] tracing: Remove backup instance after read all Masami Hiramatsu (Google) @ 2026-01-20 1:09 ` Masami Hiramatsu (Google) 2026-01-20 1:09 ` [PATCH v4 2/4] tracing: Make the backup instance non-reusable Masami Hiramatsu (Google) ` (2 subsequent siblings) 3 siblings, 0 replies; 6+ messages in thread From: Masami Hiramatsu (Google) @ 2026-01-20 1:09 UTC (permalink / raw) To: Steven Rostedt Cc: Masami Hiramatsu, Mathieu Desnoyers, linux-kernel, linux-trace-kernel From: Masami Hiramatsu (Google) <mhiramat@kernel.org> 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) <mhiramat@kernel.org> --- kernel/trace/trace.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 38f7a7a55c23..5ddaeced9cb3 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4873,6 +4873,8 @@ static int tracing_single_release_tr(struct inode *inode, struct file *file) return single_release(inode, file); } +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 = inode->i_private; @@ -4897,6 +4899,8 @@ static int tracing_open(struct inode *inode, struct file *file) tracing_reset_online_cpus(trace_buf); else tracing_reset_cpu(trace_buf, cpu); + + update_last_data_if_empty(tr); } if (file->f_mode & FMODE_READ) { @@ -5963,6 +5967,7 @@ 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); } @@ -7781,6 +7786,7 @@ int tracing_set_clock(struct trace_array *tr, const char *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); if (tr->scratch && !(tr->flags & TRACE_ARRAY_FL_LAST_BOOT)) { struct trace_scratch *tscratch = tr->scratch; @@ -8018,6 +8024,7 @@ 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; } ^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH v4 2/4] tracing: Make the backup instance non-reusable 2026-01-20 1:09 [PATCH v4 0/4] tracing: Remove backup instance after read all Masami Hiramatsu (Google) 2026-01-20 1:09 ` [PATCH v4 1/4] tracing: Reset last_boot_info if ring buffer is reset Masami Hiramatsu (Google) @ 2026-01-20 1:09 ` Masami Hiramatsu (Google) 2026-01-20 8:17 ` kernel test robot 2026-01-20 1:09 ` [PATCH v4 3/4] tracing: Remove the backup instance automatically after read Masami Hiramatsu (Google) 2026-01-20 1:09 ` [PATCH v4 4/4] tracing/Documentation: Add a section about backup instance Masami Hiramatsu (Google) 3 siblings, 1 reply; 6+ messages in thread From: Masami Hiramatsu (Google) @ 2026-01-20 1:09 UTC (permalink / raw) To: Steven Rostedt Cc: Masami Hiramatsu, Mathieu Desnoyers, linux-kernel, linux-trace-kernel From: Masami Hiramatsu (Google) <mhiramat@kernel.org> 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) <mhiramat@kernel.org> --- 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 | 93 ++++++++++++++++++++++++++++++------------- kernel/trace/trace.h | 8 +++- kernel/trace/trace_boot.c | 5 +- kernel/trace/trace_events.c | 68 +++++++++++++++++++------------ 4 files changed, 117 insertions(+), 57 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 5ddaeced9cb3..b27e1cdeffb0 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5034,6 +5034,11 @@ static ssize_t tracing_write_stub(struct file *filp, const char __user *ubuf, size_t count, loff_t *ppos) { + struct trace_array *tr = file_inode(filp)->i_private; + + if (trace_array_is_readonly(tr)) + return -EPERM; + return count; } @@ -5134,6 +5139,9 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf, cpumask_var_t tracing_cpumask_new; int err; + if (trace_array_is_readonly(tr)) + return -EPERM; + if (count == 0 || count > KMALLOC_MAX_SIZE) return -EINVAL; @@ -6418,6 +6426,9 @@ tracing_set_trace_write(struct file *filp, const char __user *ubuf, size_t ret; int err; + if (trace_array_is_readonly(tr)) + return -EPERM; + ret = cnt; if (cnt > MAX_TRACER_SIZE) @@ -7052,6 +7063,9 @@ tracing_entries_write(struct file *filp, const char __user *ubuf, unsigned long val; int ret; + if (trace_array_is_readonly(tr)) + return -EPERM; + ret = kstrtoul_from_user(ubuf, cnt, 10, &val); if (ret) return ret; @@ -7806,6 +7820,9 @@ static ssize_t tracing_clock_write(struct file *filp, const char __user *ubuf, const char *clockstr; int ret; + if (trace_array_is_readonly(tr)) + return -EPERM; + if (cnt >= sizeof(buf)) return -EINVAL; @@ -9360,12 +9377,16 @@ static void tracing_init_tracefs_percpu(struct trace_array *tr, long cpu) { struct dentry *d_percpu = tracing_dentry_percpu(tr, cpu); + umode_t writable_mode = TRACE_MODE_WRITE; struct dentry *d_cpu; char cpu_dir[30]; /* 30 characters should be more than enough */ if (!d_percpu) return; + if (trace_array_is_readonly(tr)) + writable_mode = TRACE_MODE_READ; + snprintf(cpu_dir, 30, "cpu%ld", cpu); d_cpu = tracefs_create_dir(cpu_dir, d_percpu); if (!d_cpu) { @@ -9588,7 +9609,6 @@ struct dentry *trace_create_file(const char *name, return ret; } - static struct dentry *trace_options_init_dentry(struct trace_array *tr) { struct dentry *d_tracer; @@ -9818,6 +9838,9 @@ rb_simple_write(struct file *filp, const char __user *ubuf, unsigned long val; int ret; + if (trace_array_is_readonly(tr)) + return -EPERM; + ret = kstrtoul_from_user(ubuf, cnt, 10, &val); if (ret) return ret; @@ -9924,6 +9947,9 @@ buffer_subbuf_size_write(struct file *filp, const char __user *ubuf, int pages; int ret; + if (trace_array_is_readonly(tr)) + return -EPERM; + ret = kstrtoul_from_user(ubuf, cnt, 10, &val); if (ret) return ret; @@ -10604,17 +10630,23 @@ 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 = TRACE_MODE_WRITE; + bool readonly = trace_array_is_readonly(tr); int cpu; + if (readonly) + writable_mode = TRACE_MODE_READ; + trace_create_file("available_tracers", TRACE_MODE_READ, d_tracer, - tr, &show_traces_fops); + tr, &show_traces_fops); - 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); - trace_create_file("tracing_cpumask", TRACE_MODE_WRITE, d_tracer, + trace_create_file("tracing_cpumask", writable_mode, d_tracer, tr, &tracing_cpumask_fops); + /* 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); @@ -10624,27 +10656,35 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer) trace_create_file("trace_pipe", TRACE_MODE_READ, d_tracer, tr, &tracing_pipe_fops); - 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); trace_create_file("buffer_total_size_kb", TRACE_MODE_READ, d_tracer, tr, &tracing_total_entries_fops); - 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); - trace_create_file("trace_marker", 0220, d_tracer, - tr, &tracing_mark_fops); + trace_create_file("trace_marker", 0220, d_tracer, + tr, &tracing_mark_fops); - tr->trace_marker_file = __find_event_file(tr, "ftrace", "print"); + tr->trace_marker_file = __find_event_file(tr, "ftrace", "print"); - 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); - trace_create_file("trace_clock", TRACE_MODE_WRITE, d_tracer, tr, + trace_create_file("buffer_percent", TRACE_MODE_WRITE, d_tracer, + tr, &buffer_percent_fops); + + trace_create_file("syscall_user_buf_size", TRACE_MODE_WRITE, d_tracer, + tr, &tracing_syscall_buf_fops); + } + + trace_create_file("trace_clock", writable_mode, d_tracer, tr, &trace_clock_fops); - trace_create_file("tracing_on", TRACE_MODE_WRITE, d_tracer, + trace_create_file("tracing_on", writable_mode, d_tracer, tr, &rb_simple_fops); trace_create_file("timestamp_mode", TRACE_MODE_READ, d_tracer, tr, @@ -10652,41 +10692,38 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer) tr->buffer_percent = 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, + trace_create_file("buffer_subbuf_size_kb", writable_mode, d_tracer, tr, &buffer_subbuf_size_fops); - trace_create_file("syscall_user_buf_size", TRACE_MODE_WRITE, d_tracer, - tr, &tracing_syscall_buf_fops); - create_trace_options_dir(tr); #ifdef CONFIG_TRACER_MAX_TRACE - trace_create_maxlat_file(tr, d_tracer); + if (!readonly) + trace_create_maxlat_file(tr, d_tracer); #endif - 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"); 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 { + } else if (!readonly) { trace_create_file("snapshot", TRACE_MODE_WRITE, d_tracer, tr, &snapshot_fops); #endif } - 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); for_each_tracing_cpu(cpu) tracing_init_tracefs_percpu(tr, cpu); - ftrace_init_tracefs(tr, d_tracer); + if (!readonly) + ftrace_init_tracefs(tr, d_tracer); } #ifdef CONFIG_TRACEFS_AUTOMOUNT_DEPRECATED diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index b6d42fe06115..a098011951cc 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -33,6 +33,7 @@ #define TRACE_MODE_WRITE 0640 #define TRACE_MODE_READ 0440 +#define TRACE_MODE_WRITE_MASK (TRACE_MODE_WRITE & ~TRACE_MODE_READ) enum trace_type { __TRACE_FIRST_TYPE = 0, @@ -483,6 +484,12 @@ extern bool trace_clock_in_ns(struct trace_array *tr); extern unsigned long trace_adjust_address(struct trace_array *tr, unsigned long addr); +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. @@ -681,7 +688,6 @@ struct dentry *trace_create_file(const char *name, void *data, const struct file_operations *fops); - /** * tracer_tracing_is_on_cpu - show real state of ring buffer enabled on for a cpu * @tr : the trace array to know if ring buffer is enabled 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, struct xbc_node *node) v = 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); } @@ -597,7 +598,7 @@ trace_boot_enable_tracer(struct trace_array *tr, struct xbc_node *node) p = xbc_node_find_value(node, "tracer", NULL); if (p && *p != '\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); } diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 9b07ad9eb284..5a9e03470b03 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; + if (trace_array_is_readonly(tr)) + return -EPERM; + mutex_lock(&event_mutex); ret = __ftrace_set_clr_event_nolock(tr, match, sub, event, set, mod); mutex_unlock(&event_mutex); @@ -2817,8 +2820,8 @@ event_subsystem_dir(struct trace_array *tr, const char *name, } else __get_system(system); - /* ftrace only has directories no files */ - if (strcmp(name, "ftrace") == 0) + /* ftrace only has directories no files, readonly instance too. */ + if (strcmp(name, "ftrace") == 0 || trace_array_is_readonly(tr)) nr_entries = 0; else nr_entries = ARRAY_SIZE(system_entries); @@ -2983,28 +2986,30 @@ event_create_dir(struct eventfs_inode *parent, struct trace_event_file *file) int ret; static struct eventfs_entry event_entries[] = { { - .name = "enable", + .name = "format", .callback = event_callback, - .release = event_release, }, +#ifdef CONFIG_PERF_EVENTS { - .name = "filter", + .name = "id", .callback = 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_ENTRIES. */ { - .name = "trigger", + .name = "enable", .callback = event_callback, + .release = event_release, }, { - .name = "format", + .name = "filter", .callback = event_callback, }, -#ifdef CONFIG_PERF_EVENTS { - .name = "id", + .name = "trigger", .callback = event_callback, }, -#endif #ifdef CONFIG_HIST_TRIGGERS { .name = "hist", @@ -3037,9 +3042,13 @@ event_create_dir(struct eventfs_inode *parent, struct trace_event_file *file) if (!e_events) return -ENOMEM; - nr_entries = ARRAY_SIZE(event_entries); + if (trace_array_is_readonly(tr)) + nr_entries = NR_RO_EVENT_ENTRIES; + else + nr_entries = ARRAY_SIZE(event_entries); name = trace_event_name(call); + ei = eventfs_create_dir(name, e_events, event_entries, nr_entries, file); if (IS_ERR(ei)) { pr_warn("Could not create tracefs '%s' directory\n", name); @@ -4381,25 +4390,25 @@ create_event_toplevel_files(struct dentry *parent, struct trace_array *tr) int nr_entries; static struct eventfs_entry events_entries[] = { { - .name = "enable", + .name = "header_page", .callback = events_callback, }, { - .name = "header_page", + .name = "header_event", .callback = events_callback, }, +#define NR_RO_TOP_ENTRIES 2 +/* Readonly files must be above this line and counted by NR_RO_TOP_ENTRIES. */ { - .name = "header_event", + .name = "enable", .callback = events_callback, }, }; - entry = trace_create_file("set_event", TRACE_MODE_WRITE, parent, - tr, &ftrace_set_event_fops); - if (!entry) - return -ENOMEM; - - nr_entries = ARRAY_SIZE(events_entries); + if (trace_array_is_readonly(tr)) + nr_entries = NR_RO_TOP_ENTRIES; + else + nr_entries = ARRAY_SIZE(events_entries); e_events = eventfs_create_events_dir("events", parent, events_entries, nr_entries, tr); @@ -4408,15 +4417,22 @@ create_event_toplevel_files(struct dentry *parent, struct trace_array *tr) return -ENOMEM; } - /* There are not as crucial, just warn if they are not created */ + if (!trace_array_is_readonly(tr)) { - trace_create_file("set_event_pid", TRACE_MODE_WRITE, parent, - tr, &ftrace_set_event_pid_fops); + entry = trace_create_file("set_event", TRACE_MODE_WRITE, parent, + tr, &ftrace_set_event_fops); + if (!entry) + return -ENOMEM; + + /* There are not as crucial, just warn if they are not created */ - trace_create_file("set_event_notrace_pid", - TRACE_MODE_WRITE, parent, tr, - &ftrace_set_event_notrace_pid_fops); + 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 = e_events; return 0; ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v4 2/4] tracing: Make the backup instance non-reusable 2026-01-20 1:09 ` [PATCH v4 2/4] tracing: Make the backup instance non-reusable Masami Hiramatsu (Google) @ 2026-01-20 8:17 ` kernel test robot 0 siblings, 0 replies; 6+ messages in thread From: kernel test robot @ 2026-01-20 8:17 UTC (permalink / raw) To: Masami Hiramatsu (Google), Steven Rostedt Cc: oe-kbuild-all, Masami Hiramatsu, Mathieu Desnoyers, linux-kernel, linux-trace-kernel Hi Masami, kernel test robot noticed the following build warnings: [auto build test WARNING on trace/for-next] [also build test WARNING on linus/master v6.19-rc6 next-20260119] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch#_base_tree_information] url: https://github.com/intel-lab-lkp/linux/commits/Masami-Hiramatsu-Google/tracing-Reset-last_boot_info-if-ring-buffer-is-reset/20260120-091429 base: https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next patch link: https://lore.kernel.org/r/176887137556.578403.17994205756247311821.stgit%40mhiramat.tok.corp.google.com patch subject: [PATCH v4 2/4] tracing: Make the backup instance non-reusable config: arc-defconfig (https://download.01.org/0day-ci/archive/20260120/202601201531.ng4kqZhn-lkp@intel.com/config) compiler: arc-linux-gcc (GCC) 15.2.0 reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260120/202601201531.ng4kqZhn-lkp@intel.com/reproduce) If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags | Reported-by: kernel test robot <lkp@intel.com> | Closes: https://lore.kernel.org/oe-kbuild-all/202601201531.ng4kqZhn-lkp@intel.com/ All warnings (new ones prefixed by >>): kernel/trace/trace.c: In function 'tracing_init_tracefs_percpu': >> kernel/trace/trace.c:9398:17: warning: variable 'writable_mode' set but not used [-Wunused-but-set-variable] 9398 | umode_t writable_mode = TRACE_MODE_WRITE; | ^~~~~~~~~~~~~ vim +/writable_mode +9398 kernel/trace/trace.c 9393 9394 static void 9395 tracing_init_tracefs_percpu(struct trace_array *tr, long cpu) 9396 { 9397 struct dentry *d_percpu = tracing_dentry_percpu(tr, cpu); > 9398 umode_t writable_mode = TRACE_MODE_WRITE; 9399 struct dentry *d_cpu; 9400 char cpu_dir[30]; /* 30 characters should be more than enough */ 9401 9402 if (!d_percpu) 9403 return; 9404 9405 if (trace_array_is_readonly(tr)) 9406 writable_mode = TRACE_MODE_READ; 9407 9408 snprintf(cpu_dir, 30, "cpu%ld", cpu); 9409 d_cpu = tracefs_create_dir(cpu_dir, d_percpu); 9410 if (!d_cpu) { 9411 pr_warn("Could not create tracefs '%s' entry\n", cpu_dir); 9412 return; 9413 } 9414 9415 /* per cpu trace_pipe */ 9416 trace_create_cpu_file("trace_pipe", TRACE_MODE_READ, d_cpu, 9417 tr, cpu, &tracing_pipe_fops); 9418 9419 /* per cpu trace */ 9420 trace_create_cpu_file("trace", TRACE_MODE_WRITE, d_cpu, 9421 tr, cpu, &tracing_fops); 9422 9423 trace_create_cpu_file("trace_pipe_raw", TRACE_MODE_READ, d_cpu, 9424 tr, cpu, &tracing_buffers_fops); 9425 9426 trace_create_cpu_file("stats", TRACE_MODE_READ, d_cpu, 9427 tr, cpu, &tracing_stats_fops); 9428 9429 trace_create_cpu_file("buffer_size_kb", TRACE_MODE_READ, d_cpu, 9430 tr, cpu, &tracing_entries_fops); 9431 9432 if (tr->range_addr_start) 9433 trace_create_cpu_file("buffer_meta", TRACE_MODE_READ, d_cpu, 9434 tr, cpu, &tracing_buffer_meta_fops); 9435 #ifdef CONFIG_TRACER_SNAPSHOT 9436 if (!tr->range_addr_start) { 9437 trace_create_cpu_file("snapshot", TRACE_MODE_WRITE, d_cpu, 9438 tr, cpu, &snapshot_fops); 9439 9440 trace_create_cpu_file("snapshot_raw", TRACE_MODE_READ, d_cpu, 9441 tr, cpu, &snapshot_raw_fops); 9442 } 9443 #endif 9444 } 9445 -- 0-DAY CI Kernel Test Service https://github.com/intel/lkp-tests/wiki ^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v4 3/4] tracing: Remove the backup instance automatically after read 2026-01-20 1:09 [PATCH v4 0/4] tracing: Remove backup instance after read all Masami Hiramatsu (Google) 2026-01-20 1:09 ` [PATCH v4 1/4] tracing: Reset last_boot_info if ring buffer is reset Masami Hiramatsu (Google) 2026-01-20 1:09 ` [PATCH v4 2/4] tracing: Make the backup instance non-reusable Masami Hiramatsu (Google) @ 2026-01-20 1:09 ` Masami Hiramatsu (Google) 2026-01-20 1:09 ` [PATCH v4 4/4] tracing/Documentation: Add a section about backup instance Masami Hiramatsu (Google) 3 siblings, 0 replies; 6+ messages in thread From: Masami Hiramatsu (Google) @ 2026-01-20 1:09 UTC (permalink / raw) To: Steven Rostedt Cc: Masami Hiramatsu, Mathieu Desnoyers, linux-kernel, linux-trace-kernel From: Masami Hiramatsu (Google) <mhiramat@kernel.org> 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) <mhiramat@kernel.org> --- Changes in v4: - Update description. --- kernel/trace/trace.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++- kernel/trace/trace.h | 6 +++++ 2 files changed, 69 insertions(+), 1 deletion(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index b27e1cdeffb0..7fa0809cd71b 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -590,6 +590,55 @@ void trace_set_ring_buffer_expanded(struct trace_array *tr) tr->ring_buffer_expanded = true; } +static int __remove_instance(struct trace_array *tr); + +static void trace_array_autoremove(struct work_struct *work) +{ + struct trace_array *tr = container_of(work, struct trace_array, autoremove_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 the result. + */ + __remove_instance(tr); +} + +static struct workqueue_struct *autoremove_wq; + +static void trace_array_init_autoremove(struct trace_array *tr) +{ + INIT_WORK(&tr->autoremove_work, trace_array_autoremove); +} + +static void trace_array_kick_autoremove(struct trace_array *tr) +{ + if (!work_pending(&tr->autoremove_work) && autoremove_wq) + queue_work(autoremove_wq, &tr->autoremove_work); +} + +static void trace_array_cancel_autoremove(struct trace_array *tr) +{ + if (work_pending(&tr->autoremove_work)) + cancel_work(&tr->autoremove_work); +} + +__init static int trace_array_init_autoremove_wq(void) +{ + autoremove_wq = alloc_workqueue("tr_autoremove_wq", + WQ_UNBOUND | WQ_HIGHPRI, 0); + if (!autoremove_wq) { + pr_err("Unable to allocate tr_autoremove_wq\n"); + return -ENOMEM; + } + return 0; +} + +late_initcall_sync(trace_array_init_autoremove_wq); + LIST_HEAD(ftrace_trace_arrays); int trace_array_get(struct trace_array *this_tr) @@ -598,7 +647,7 @@ 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 == this_tr) { + if (tr == this_tr && !tr->free_on_close) { tr->ref++; return 0; } @@ -611,6 +660,12 @@ 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 == 1 && this_tr->free_on_close) + trace_array_kick_autoremove(this_tr); } /** @@ -6219,6 +6274,10 @@ static void update_last_data(struct trace_array *tr) /* Only if the buffer has previous boot data clear and update it. */ tr->flags &= ~TRACE_ARRAY_FL_LAST_BOOT; + /* If this is a backup instance, mark it for autoremove. */ + if (tr->flags & TRACE_ARRAY_FL_VMALLOC) + tr->free_on_close = true; + /* Reset the module list and reload them */ if (tr->scratch) { struct trace_scratch *tscratch = tr->scratch; @@ -10390,6 +10449,8 @@ trace_array_create_systems(const char *name, const char *systems, if (ftrace_allocate_ftrace_ops(tr) < 0) goto out_free_tr; + trace_array_init_autoremove(tr); + ftrace_init_trace_array(tr); init_trace_flags_index(tr); @@ -10538,6 +10599,7 @@ static int __remove_instance(struct trace_array *tr) if (update_marker_trace(tr, 0)) synchronize_rcu(); + 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 a098011951cc..947f641a9cf0 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -447,6 +447,12 @@ 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; }; enum { ^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH v4 4/4] tracing/Documentation: Add a section about backup instance 2026-01-20 1:09 [PATCH v4 0/4] tracing: Remove backup instance after read all Masami Hiramatsu (Google) ` (2 preceding siblings ...) 2026-01-20 1:09 ` [PATCH v4 3/4] tracing: Remove the backup instance automatically after read Masami Hiramatsu (Google) @ 2026-01-20 1:09 ` Masami Hiramatsu (Google) 3 siblings, 0 replies; 6+ messages in thread From: Masami Hiramatsu (Google) @ 2026-01-20 1:09 UTC (permalink / raw) To: Steven Rostedt Cc: Masami Hiramatsu, Mathieu Desnoyers, linux-kernel, linux-trace-kernel From: Masami Hiramatsu (Google) <mhiramat@kernel.org> Add a section about backup instance to the debugging.rst. Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> --- Documentation/trace/debugging.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/trace/debugging.rst b/Documentation/trace/debugging.rst index 4d88c346fc38..73e2154bcf98 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 recommended 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 the +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=12M:4096:trace trace_instance=boot_map@trace,sched,irq trace_instance=backup=boot_map + +When the boot up, the previous data in the`boot_map` is copied to "backup" +instance, and the "sched:*" and "irq:*" events for current boot are traced on +"boot_map". Thus user can read the previous boot data from the "backup" instance +without stopping trace. + +Note that this "backup" instance is readonly, and will be removed automatically +if you clear the trace data or read out all trace data from "trace_pipe" or +"trace_pipe_raw" files. \ No newline at end of file ^ permalink raw reply related [flat|nested] 6+ messages in thread
end of thread, other threads:[~2026-01-20 8:17 UTC | newest] Thread overview: 6+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2026-01-20 1:09 [PATCH v4 0/4] tracing: Remove backup instance after read all Masami Hiramatsu (Google) 2026-01-20 1:09 ` [PATCH v4 1/4] tracing: Reset last_boot_info if ring buffer is reset Masami Hiramatsu (Google) 2026-01-20 1:09 ` [PATCH v4 2/4] tracing: Make the backup instance non-reusable Masami Hiramatsu (Google) 2026-01-20 8:17 ` kernel test robot 2026-01-20 1:09 ` [PATCH v4 3/4] tracing: Remove the backup instance automatically after read Masami Hiramatsu (Google) 2026-01-20 1:09 ` [PATCH v4 4/4] tracing/Documentation: Add a section about backup instance Masami Hiramatsu (Google)
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