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Commit ac99c58c authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Ingo Molnar
Browse files

tracing/syscalls: fix missing release of tracing 



Impact: fix 'stuck' syscall tracer

The syscall tracer uses a refcounter to enable several users
simultaneously.

But the refcounter did not behave correctly and always restored
its value to 0 after calling start_syscall_tracing(). Therefore,
stop_syscall_tracing() couldn't release correctly the tasks from
tracing.

Also the tracer forgot to reset the buffer when it is released.

Drop the pointless refcount decrement on start_syscall_tracing()
and reset the buffer when we release the tracer.

This fixes two reported issue:

- when we switch from syscall tracer to another tracer, syscall
  tracing continued.

- incorrect use of the refcount.

Reported-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reported-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237151439-6755-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 7243f214

kernel/trace/trace_syscalls.c

+5 −6
Original line number Diff line number Diff line
@@ -96,8 +96,9 @@ void start_ftrace_syscalls(void) 
	unsigned long flags;

	struct task_struct *g, *t;



	/* Don't enable the flag on the tasks twice */

	if (atomic_inc_return(&refcount) != 1)

		goto out;

		return;



	arch_init_ftrace_syscalls();

	read_lock_irqsave(&tasklist_lock, flags);
@@ -107,8 +108,6 @@ void start_ftrace_syscalls(void) 
	} while_each_thread(g, t);



	read_unlock_irqrestore(&tasklist_lock, flags);

out:

	atomic_dec(&refcount);

}



void stop_ftrace_syscalls(void)
@@ -116,8 +115,9 @@ void stop_ftrace_syscalls(void) 
	unsigned long flags;

	struct task_struct *g, *t;



	/* There are perhaps still some users */

	if (atomic_dec_return(&refcount))

		goto out;

		return;



	read_lock_irqsave(&tasklist_lock, flags);
@@ -126,8 +126,6 @@ void stop_ftrace_syscalls(void) 
	} while_each_thread(g, t);



	read_unlock_irqrestore(&tasklist_lock, flags);

out:

	atomic_inc(&refcount);

}



void ftrace_syscall_enter(struct pt_regs *regs)
@@ -201,6 +199,7 @@ static int init_syscall_tracer(struct trace_array *tr) 
static void reset_syscall_tracer(struct trace_array *tr)

{

	stop_ftrace_syscalls();

	tracing_reset_online_cpus(tr);

}



static struct trace_event syscall_enter_event = {