1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
3 * lttng-context-preemptible.c
5 * LTTng preemptible context.
7 * Copyright (C) 2009-2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
10 #include <linux/module.h>
11 #include <linux/slab.h>
12 #include <linux/sched.h>
13 #include <linux/irqflags.h>
14 #include <lttng/events.h>
15 #include <lttng/events-internal.h>
16 #include <ringbuffer/frontend_types.h>
17 #include <wrapper/vmalloc.h>
18 #include <lttng/tracer.h>
21 * We nest twice in preempt disabling within LTTng: one nesting is done
22 * by the instrumentation (tracepoint, kprobes, kretprobes, syscall
23 * tracepoint), and the second is within the lib ring buffer
24 * lib_ring_buffer_get_cpu().
26 #define LTTNG_PREEMPT_DISABLE_NESTING 2
29 size_t preemptible_get_size(void *priv
, struct lttng_kernel_probe_ctx
*probe_ctx
, size_t offset
)
33 size
+= lib_ring_buffer_align(offset
, lttng_alignof(uint8_t));
34 size
+= sizeof(uint8_t);
39 void preemptible_record(void *priv
, struct lttng_kernel_probe_ctx
*probe_ctx
,
40 struct lttng_kernel_ring_buffer_ctx
*ctx
,
41 struct lttng_channel
*chan
)
43 int pc
= preempt_count();
44 uint8_t preemptible
= 0;
46 WARN_ON_ONCE(pc
< LTTNG_PREEMPT_DISABLE_NESTING
);
47 if (pc
== LTTNG_PREEMPT_DISABLE_NESTING
)
49 lib_ring_buffer_align_ctx(ctx
, lttng_alignof(preemptible
));
50 chan
->ops
->event_write(ctx
, &preemptible
, sizeof(preemptible
));
54 void preemptible_get_value(void *priv
,
55 struct lttng_kernel_probe_ctx
*lttng_probe_ctx
,
56 struct lttng_ctx_value
*value
)
58 int pc
= preempt_count();
60 WARN_ON_ONCE(pc
< LTTNG_PREEMPT_DISABLE_NESTING
);
61 if (pc
== LTTNG_PREEMPT_DISABLE_NESTING
)
67 static const struct lttng_kernel_ctx_field
*ctx_field
= lttng_kernel_static_ctx_field(
68 lttng_kernel_static_event_field("preemptible",
69 lttng_kernel_static_type_integer_from_type(uint8_t, __BYTE_ORDER
, 10),
73 preemptible_get_value
,
76 int lttng_add_preemptible_to_ctx(struct lttng_kernel_ctx
**ctx
)
80 if (lttng_kernel_find_context(*ctx
, ctx_field
->event_field
->name
))
82 ret
= lttng_kernel_context_append(ctx
, ctx_field
);
83 wrapper_vmalloc_sync_mappings();
86 EXPORT_SYMBOL_GPL(lttng_add_preemptible_to_ctx
);