tracing: Allocate the ftrace event profile buffer dynamically
Currently the trace event profile buffer is allocated in the stack. But
this may be too much for the stack, as the events can have large
statically defined field size and can also grow with dynamic arrays.
Allocate two per cpu buffer for all profiled events. The first cpu
buffer is used to host every non-nmi context traces. It is protected
by disabling the interrupts while writing and committing the trace.
The second buffer is reserved for nmi. So that there is no race between
them and the first buffer.
The whole write/commit section is rcu protected because we release
these buffers while deactivating the last profiling trace event.
v2: Move the buffers from trace_event to be global, as pointed by
Steven Rostedt.
v3: Fix the syscall events to handle the profiling buffer races
by disabling interrupts, now that the buffers are globals.
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 8712ce3..7a3550c 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -384,10 +384,13 @@
static void prof_syscall_enter(struct pt_regs *regs, long id)
{
- struct syscall_trace_enter *rec;
struct syscall_metadata *sys_data;
+ struct syscall_trace_enter *rec;
+ unsigned long flags;
+ char *raw_data;
int syscall_nr;
int size;
+ int cpu;
syscall_nr = syscall_get_nr(current, regs);
if (!test_bit(syscall_nr, enabled_prof_enter_syscalls))
@@ -402,20 +405,38 @@
size = ALIGN(size + sizeof(u32), sizeof(u64));
size -= sizeof(u32);
- do {
- char raw_data[size];
+ if (WARN_ONCE(size > FTRACE_MAX_PROFILE_SIZE,
+ "profile buffer not large enough"))
+ return;
- /* zero the dead bytes from align to not leak stack to user */
- *(u64 *)(&raw_data[size - sizeof(u64)]) = 0ULL;
+ /* Protect the per cpu buffer, begin the rcu read side */
+ local_irq_save(flags);
- rec = (struct syscall_trace_enter *) raw_data;
- tracing_generic_entry_update(&rec->ent, 0, 0);
- rec->ent.type = sys_data->enter_id;
- rec->nr = syscall_nr;
- syscall_get_arguments(current, regs, 0, sys_data->nb_args,
- (unsigned long *)&rec->args);
- perf_tpcounter_event(sys_data->enter_id, 0, 1, rec, size);
- } while(0);
+ cpu = smp_processor_id();
+
+ if (in_nmi())
+ raw_data = rcu_dereference(trace_profile_buf_nmi);
+ else
+ raw_data = rcu_dereference(trace_profile_buf);
+
+ if (!raw_data)
+ goto end;
+
+ raw_data = per_cpu_ptr(raw_data, cpu);
+
+ /* zero the dead bytes from align to not leak stack to user */
+ *(u64 *)(&raw_data[size - sizeof(u64)]) = 0ULL;
+
+ rec = (struct syscall_trace_enter *) raw_data;
+ tracing_generic_entry_update(&rec->ent, 0, 0);
+ rec->ent.type = sys_data->enter_id;
+ rec->nr = syscall_nr;
+ syscall_get_arguments(current, regs, 0, sys_data->nb_args,
+ (unsigned long *)&rec->args);
+ perf_tpcounter_event(sys_data->enter_id, 0, 1, rec, size);
+
+end:
+ local_irq_restore(flags);
}
int reg_prof_syscall_enter(char *name)
@@ -460,8 +481,12 @@
static void prof_syscall_exit(struct pt_regs *regs, long ret)
{
struct syscall_metadata *sys_data;
- struct syscall_trace_exit rec;
+ struct syscall_trace_exit *rec;
+ unsigned long flags;
int syscall_nr;
+ char *raw_data;
+ int size;
+ int cpu;
syscall_nr = syscall_get_nr(current, regs);
if (!test_bit(syscall_nr, enabled_prof_exit_syscalls))
@@ -471,12 +496,46 @@
if (!sys_data)
return;
- tracing_generic_entry_update(&rec.ent, 0, 0);
- rec.ent.type = sys_data->exit_id;
- rec.nr = syscall_nr;
- rec.ret = syscall_get_return_value(current, regs);
+ /* We can probably do that at build time */
+ size = ALIGN(sizeof(*rec) + sizeof(u32), sizeof(u64));
+ size -= sizeof(u32);
- perf_tpcounter_event(sys_data->exit_id, 0, 1, &rec, sizeof(rec));
+ /*
+ * Impossible, but be paranoid with the future
+ * How to put this check outside runtime?
+ */
+ if (WARN_ONCE(size > FTRACE_MAX_PROFILE_SIZE,
+ "exit event has grown above profile buffer size"))
+ return;
+
+ /* Protect the per cpu buffer, begin the rcu read side */
+ local_irq_save(flags);
+ cpu = smp_processor_id();
+
+ if (in_nmi())
+ raw_data = rcu_dereference(trace_profile_buf_nmi);
+ else
+ raw_data = rcu_dereference(trace_profile_buf);
+
+ if (!raw_data)
+ goto end;
+
+ raw_data = per_cpu_ptr(raw_data, cpu);
+
+ /* zero the dead bytes from align to not leak stack to user */
+ *(u64 *)(&raw_data[size - sizeof(u64)]) = 0ULL;
+
+ rec = (struct syscall_trace_exit *)raw_data;
+
+ tracing_generic_entry_update(&rec->ent, 0, 0);
+ rec->ent.type = sys_data->exit_id;
+ rec->nr = syscall_nr;
+ rec->ret = syscall_get_return_value(current, regs);
+
+ perf_tpcounter_event(sys_data->exit_id, 0, 1, rec, size);
+
+end:
+ local_irq_restore(flags);
}
int reg_prof_syscall_exit(char *name)