From nobody Wed Feb 11 05:40:59 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 1A2D92EB87F for ; Mon, 9 Feb 2026 02:20:09 +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=1770603609; cv=none; b=K7THMXAq6zPF7WB06cEExzHFahmpJtAxmMbqRHOnxjHjGBIxZdERmAYy+epOh8kCYQsgIWGi2AIk8NH1HuGxFAaYqtaNUWUVelxAxVIR4jfFbDbDWzcYdEnYxmppOV14MpTmuPNxz+aXyHGRDwLXiH8723/uH17TOY3mhBbDK88= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770603609; c=relaxed/simple; bh=hackC6XcyM/M+opMUK5WvhB6XXKw3kL10CqCaucSXWA=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=CwpUQrR0mKp83AttZvGRLhIosNHLTHGrAS5Ixu1+lsGc4dP5ltoHISowT3FI8HkvMzJ68R7hKly8aRRLCFWSGgM9QzDiSQkkg7tiflURlOJkVnCPX68I+hOZNWRpy/5jlM5JYIsUttc70x5oUTOBksDYN5fM8ou77z45sjgFaYw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rYgQfhCb; 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="rYgQfhCb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D1384C2BCAF; Mon, 9 Feb 2026 02:20:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770603609; bh=hackC6XcyM/M+opMUK5WvhB6XXKw3kL10CqCaucSXWA=; h=Date:From:To:Cc:Subject:References:From; b=rYgQfhCb5tWVFpawra6ooIrnNxUH6bxgmqh5qeGBwkP+tbd+R1DLpfmyJxCkBnFvI uroXgnl1rXGRsFeLwdqcYSFm3MPfXuxbfWH243TaAuxtDXdEax8/BjK7LZwK2/266/ v7GwECZaK2VZxETm2tXPq8IDS/jTx/ZDteKNgdgWjC/F31EjTFLTB0umsVoKCUOIil 7ctmW4u3E2GgV13CBQ2w8/QMDlFbDCnyh0zwTcdbP4dWY0ukEq6ViXQsurN/LTfUXQ CgyJ7jx+9KYXwXal8xMI3KIOBWX3qf1xC7SOpawAjWurxsRWWsxpe7o9q4fpOED6aM FAfFrMhstVX/g== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1vpGtT-0000000Aa9s-22Ve; Sun, 08 Feb 2026 21:20:55 -0500 Message-ID: <20260209022055.341867623@kernel.org> User-Agent: quilt/0.68 Date: Sun, 08 Feb 2026 21:20:46 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton Subject: [for-next][PATCH 20/20] tracing: Better separate SNAPSHOT and MAX_TRACE options References: <20260209022026.627895421@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Steven Rostedt The latency tracers (scheduler, irqsoff, etc) were created when tracing was first added. These tracers required a "snapshot" buffer that was the same size as the ring buffer being written to. When a new max latency was hit, the main ring buffer would swap with the snapshot buffer so that the trace leading up to the latency would be saved in the snapshot buffer (The snapshot buffer is never written to directly and the data within it can be viewed without fear of being overwritten). Later, a new feature was added to allow snapshots to be taken by user space or even event triggers. This created a "snapshot" file that allowed users to trigger a snapshot from user space to save the current trace. The config for this new feature (CONFIG_TRACER_SNAPSHOT) would select the latency tracer config (CONFIG_TRACER_MAX_LATENCY) as it would need all the functionality from it as it already existed. But this was incorrect. As the snapshot feature is really what the latency tracers need and not the other way around. Have CONFIG_TRACER_MAX_TRACE select CONFIG_TRACER_SNAPSHOT where the tracers that needs the max latency buffer selects the TRACE_MAX_TRACE which will then select TRACER_SNAPSHOT. Also, go through trace.c and trace.h and make the code that only needs the TRACER_MAX_TRACE protected by that and the code that always requires the snapshot to be protected by TRACER_SNAPSHOT. Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Link: https://patch.msgid.link/20260208183856.767870992@kernel.org Signed-off-by: Steven Rostedt (Google) --- kernel/trace/Kconfig | 8 ++--- kernel/trace/trace.c | 73 +++++++++++++++++++++++--------------------- kernel/trace/trace.h | 19 +++++++----- 3 files changed, 53 insertions(+), 47 deletions(-) diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index bfa2ec46e075..bedb2f982823 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -133,6 +133,7 @@ config BUILDTIME_MCOUNT_SORT =20 config TRACER_MAX_TRACE bool + select TRACER_SNAPSHOT =20 config TRACE_CLOCK bool @@ -422,7 +423,6 @@ config IRQSOFF_TRACER select GENERIC_TRACER select TRACER_MAX_TRACE select RING_BUFFER_ALLOW_SWAP - select TRACER_SNAPSHOT select TRACER_SNAPSHOT_PER_CPU_SWAP help This option measures the time spent in irqs-off critical @@ -445,7 +445,6 @@ config PREEMPT_TRACER select GENERIC_TRACER select TRACER_MAX_TRACE select RING_BUFFER_ALLOW_SWAP - select TRACER_SNAPSHOT select TRACER_SNAPSHOT_PER_CPU_SWAP select TRACE_PREEMPT_TOGGLE help @@ -467,7 +466,6 @@ config SCHED_TRACER select GENERIC_TRACER select CONTEXT_SWITCH_TRACER select TRACER_MAX_TRACE - select TRACER_SNAPSHOT help This tracer tracks the latency of the highest priority task to be scheduled in, starting from the point it has woken up. @@ -617,7 +615,6 @@ config TRACE_SYSCALL_BUF_SIZE_DEFAULT =20 config TRACER_SNAPSHOT bool "Create a snapshot trace buffer" - select TRACER_MAX_TRACE help Allow tracing users to take snapshot of the current buffer using the ftrace interface, e.g.: @@ -625,6 +622,9 @@ config TRACER_SNAPSHOT echo 1 > /sys/kernel/tracing/snapshot cat snapshot =20 + Note, the latency tracers select this option. To disable it, + all the latency tracers need to be disabled. + config TRACER_SNAPSHOT_PER_CPU_SWAP bool "Allow snapshot to swap per CPU" depends on TRACER_SNAPSHOT diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 405212166677..845b8a165daf 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -825,15 +825,15 @@ static void tracing_snapshot_instance_cond(struct tra= ce_array *tr, return; } =20 - /* Note, snapshot can not be used when the tracer uses it */ - if (tracer_uses_snapshot(tr->current_trace)) { - trace_array_puts(tr, "*** LATENCY TRACER ACTIVE ***\n"); + if (tr->mapped) { + trace_array_puts(tr, "*** BUFFER MEMORY MAPPED ***\n"); trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n"); return; } =20 - if (tr->mapped) { - trace_array_puts(tr, "*** BUFFER MEMORY MAPPED ***\n"); + /* Note, snapshot can not be used when the tracer uses it */ + if (tracer_uses_snapshot(tr->current_trace)) { + trace_array_puts(tr, "*** LATENCY TRACER ACTIVE ***\n"); trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n"); return; } @@ -1555,8 +1555,8 @@ static void __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu) { struct array_buffer *trace_buf =3D &tr->array_buffer; - struct array_buffer *max_buf =3D &tr->snapshot_buffer; struct trace_array_cpu *data =3D per_cpu_ptr(trace_buf->data, cpu); + struct array_buffer *max_buf =3D &tr->snapshot_buffer; struct trace_array_cpu *max_data =3D per_cpu_ptr(max_buf->data, cpu); =20 max_buf->cpu =3D cpu; @@ -1585,7 +1585,14 @@ __update_max_tr(struct trace_array *tr, struct task_= struct *tsk, int cpu) tracing_record_cmdline(tsk); latency_fsnotify(tr); } +#else +static inline void trace_create_maxlat_file(struct trace_array *tr, + struct dentry *d_tracer) { } +static inline void __update_max_tr(struct trace_array *tr, + struct task_struct *tsk, int cpu) { } +#endif /* CONFIG_TRACER_MAX_TRACE */ =20 +#ifdef CONFIG_TRACER_SNAPSHOT /** * update_max_tr - snapshot all trace buffers from global_trace to max_tr * @tr: tracer @@ -1619,12 +1626,11 @@ update_max_tr(struct trace_array *tr, struct task_s= truct *tsk, int cpu, else ring_buffer_record_off(tr->snapshot_buffer.buffer); =20 -#ifdef CONFIG_TRACER_SNAPSHOT if (tr->cond_snapshot && !tr->cond_snapshot->update(tr, cond_data)) { arch_spin_unlock(&tr->max_lock); return; } -#endif + swap(tr->array_buffer.buffer, tr->snapshot_buffer.buffer); =20 __update_max_tr(tr, tsk, cpu); @@ -1679,10 +1685,7 @@ update_max_tr_single(struct trace_array *tr, struct = task_struct *tsk, int cpu) __update_max_tr(tr, tsk, cpu); arch_spin_unlock(&tr->max_lock); } -#else /* !CONFIG_TRACER_MAX_TRACE */ -static inline void trace_create_maxlat_file(struct trace_array *tr, - struct dentry *d_tracer) { } -#endif /* CONFIG_TRACER_MAX_TRACE */ +#endif /* CONFIG_TRACER_SNAPSHOT */ =20 struct pipe_wait { struct trace_iterator *iter; @@ -1715,7 +1718,7 @@ static int wait_on_pipe(struct trace_iterator *iter, = int full) ret =3D ring_buffer_wait(iter->array_buffer->buffer, iter->cpu_file, full, wait_pipe_cond, &pwait); =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT /* * Make sure this is still the snapshot buffer, as if a snapshot were * to happen, this would now be the main buffer. @@ -2058,7 +2061,7 @@ void tracing_reset_all_online_cpus_unlocked(void) continue; tr->clear_trace =3D false; tracing_reset_online_cpus(&tr->array_buffer); -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT tracing_reset_online_cpus(&tr->snapshot_buffer); #endif } @@ -2098,7 +2101,7 @@ static void tracing_start_tr(struct trace_array *tr) if (buffer) ring_buffer_record_enable(buffer); =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT buffer =3D tr->snapshot_buffer.buffer; if (buffer) ring_buffer_record_enable(buffer); @@ -2134,7 +2137,7 @@ static void tracing_stop_tr(struct trace_array *tr) if (buffer) ring_buffer_record_disable(buffer); =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT buffer =3D tr->snapshot_buffer.buffer; if (buffer) ring_buffer_record_disable(buffer); @@ -3757,7 +3760,7 @@ static void test_ftrace_alive(struct seq_file *m) "# MAY BE MISSING FUNCTION EVENTS\n"); } =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT static void show_snapshot_main_help(struct seq_file *m) { seq_puts(m, "# echo 0 > snapshot : Clears and frees snapshot buffer\n" @@ -3935,7 +3938,7 @@ __tracing_open(struct inode *inode, struct file *file= , bool snapshot) =20 iter->tr =3D tr; =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT /* Currently only the top directory has a snapshot */ if (tr->current_trace->print_max || snapshot) iter->array_buffer =3D &tr->snapshot_buffer; @@ -4351,14 +4354,14 @@ int tracing_set_cpumask(struct trace_array *tr, if (cpumask_test_cpu(cpu, tr->tracing_cpumask) && !cpumask_test_cpu(cpu, tracing_cpumask_new)) { ring_buffer_record_disable_cpu(tr->array_buffer.buffer, cpu); -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT ring_buffer_record_disable_cpu(tr->snapshot_buffer.buffer, cpu); #endif } if (!cpumask_test_cpu(cpu, tr->tracing_cpumask) && cpumask_test_cpu(cpu, tracing_cpumask_new)) { ring_buffer_record_enable_cpu(tr->array_buffer.buffer, cpu); -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT ring_buffer_record_enable_cpu(tr->snapshot_buffer.buffer, cpu); #endif } @@ -4568,7 +4571,7 @@ int set_tracer_flag(struct trace_array *tr, u64 mask,= int enabled) =20 case TRACE_ITER(OVERWRITE): ring_buffer_change_overwrite(tr->array_buffer.buffer, enabled); -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT ring_buffer_change_overwrite(tr->snapshot_buffer.buffer, enabled); #endif break; @@ -5232,7 +5235,7 @@ static void update_buffer_entries(struct array_buffer= *buf, int cpu) } } =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT /* resize @tr's buffer to the size of @size_tr's entries */ static int resize_buffer_duplicate_size(struct array_buffer *trace_buf, struct array_buffer *size_buf, int cpu_id) @@ -5258,7 +5261,7 @@ static int resize_buffer_duplicate_size(struct array_= buffer *trace_buf, =20 return ret; } -#endif /* CONFIG_TRACER_MAX_TRACE */ +#endif /* CONFIG_TRACER_SNAPSHOT */ =20 static int __tracing_resize_ring_buffer(struct trace_array *tr, unsigned long size, int cpu) @@ -5283,7 +5286,7 @@ static int __tracing_resize_ring_buffer(struct trace_= array *tr, if (ret < 0) goto out_start; =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT if (!tr->allocated_snapshot) goto out; =20 @@ -5315,7 +5318,7 @@ static int __tracing_resize_ring_buffer(struct trace_= array *tr, update_buffer_entries(&tr->snapshot_buffer, cpu); =20 out: -#endif /* CONFIG_TRACER_MAX_TRACE */ +#endif /* CONFIG_TRACER_SNAPSHOT */ =20 update_buffer_entries(&tr->array_buffer, cpu); out_start: @@ -7020,7 +7023,7 @@ int tracing_set_clock(struct trace_array *tr, const c= har *clockstr) */ tracing_reset_online_cpus(&tr->array_buffer); =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT if (tr->snapshot_buffer.buffer) ring_buffer_set_clock(tr->snapshot_buffer.buffer, trace_clocks[i].func); tracing_reset_online_cpus(&tr->snapshot_buffer); @@ -8167,7 +8170,7 @@ static long tracing_buffers_ioctl(struct file *file, = unsigned int cmd, unsigned return 0; } =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT static int get_snapshot_map(struct trace_array *tr) { int err =3D 0; @@ -9171,7 +9174,7 @@ buffer_subbuf_size_write(struct file *filp, const cha= r __user *ubuf, if (ret) goto out; =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT =20 if (!tr->allocated_snapshot) goto out_max; @@ -9392,7 +9395,7 @@ static int allocate_trace_buffers(struct trace_array = *tr, int size) if (ret) return ret; =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT /* Fix mapped buffer trace arrays do not have snapshot buffers */ if (tr->range_addr_start) return 0; @@ -9419,7 +9422,7 @@ static void free_trace_buffers(struct trace_array *tr) free_trace_buffer(&tr->array_buffer); kfree(tr->module_delta); =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT free_trace_buffer(&tr->snapshot_buffer); #endif } @@ -9561,7 +9564,7 @@ trace_array_create_systems(const char *name, const ch= ar *systems, tr->syscall_buf_sz =3D global_trace.syscall_buf_sz; =20 tr->max_lock =3D (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED; -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT spin_lock_init(&tr->snapshot_trigger_lock); #endif tr->current_trace =3D &nop_trace; @@ -10515,7 +10518,7 @@ ssize_t trace_parse_run_command(struct file *file, = const char __user *buffer, return done; } =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT __init static bool tr_needs_alloc_snapshot(const char *name) { char *test; @@ -10705,7 +10708,7 @@ __init static void enable_instances(void) } } else { /* Only non mapped buffers have snapshot buffers */ - if (IS_ENABLED(CONFIG_TRACER_MAX_TRACE)) + if (IS_ENABLED(CONFIG_TRACER_SNAPSHOT)) do_allocate_snapshot(name); } =20 @@ -10832,7 +10835,7 @@ __init static int tracer_alloc_buffers(void) global_trace.current_trace_flags =3D nop_trace.flags; =20 global_trace.max_lock =3D (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED; -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT spin_lock_init(&global_trace.snapshot_trigger_lock); #endif ftrace_init_global_array_ops(&global_trace); @@ -10900,7 +10903,7 @@ struct trace_array *trace_get_global_array(void) =20 void __init ftrace_boot_snapshot(void) { -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT struct trace_array *tr; =20 if (!snapshot_at_boot) diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index ebb47abc0ee7..649fdd20fc91 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -329,7 +329,7 @@ struct trace_array { struct list_head list; char *name; struct array_buffer array_buffer; -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT /* * The snapshot_buffer is used to snapshot the trace when a maximum * latency is reached, or when the user initiates a snapshot. @@ -346,13 +346,16 @@ struct trace_array { bool allocated_snapshot; spinlock_t snapshot_trigger_lock; unsigned int snapshot; +#ifdef CONFIG_TRACER_MAX_TRACE unsigned long max_latency; #ifdef CONFIG_FSNOTIFY struct dentry *d_max_latency; struct work_struct fsnotify_work; struct irq_work fsnotify_irqwork; -#endif -#endif +#endif /* CONFIG_FSNOTIFY */ +#endif /* CONFIG_TRACER_MAX_TRACE */ +#endif /* CONFIG_TRACER_SNAPSHOT */ + /* The below is for memory mapped ring buffer */ unsigned int mapped; unsigned long range_addr_start; @@ -378,7 +381,7 @@ struct trace_array { * * It is also used in other places outside the update_max_tr * so it needs to be defined outside of the - * CONFIG_TRACER_MAX_TRACE. + * CONFIG_TRACER_SNAPSHOT. */ arch_spinlock_t max_lock; #ifdef CONFIG_FTRACE_SYSCALLS @@ -791,22 +794,22 @@ int trace_pid_write(struct trace_pid_list *filtered_p= ids, struct trace_pid_list **new_pid_list, const char __user *ubuf, size_t cnt); =20 -#ifdef CONFIG_TRACER_MAX_TRACE +#ifdef CONFIG_TRACER_SNAPSHOT void update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cp= u, void *cond_data); void update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu); =20 -#ifdef CONFIG_FSNOTIFY -#define LATENCY_FS_NOTIFY +#if defined(CONFIG_TRACER_MAX_TRACE) && defined(CONFIG_FSNOTIFY) +# define LATENCY_FS_NOTIFY #endif -#endif /* CONFIG_TRACER_MAX_TRACE */ =20 #ifdef LATENCY_FS_NOTIFY void latency_fsnotify(struct trace_array *tr); #else static inline void latency_fsnotify(struct trace_array *tr) { } #endif +#endif /* CONFIG_TRACER_SNAPSHOT */ =20 #ifdef CONFIG_STACKTRACE void __trace_stack(struct trace_array *tr, unsigned int trace_ctx, int ski= p); --=20 2.51.0