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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: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237151439-6755-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Frederic Weisbecker 2009-03-15 22:10:35 +01:00 committed by Ingo Molnar
parent 7243f2145a
commit ac99c58c9e
1 changed files with 5 additions and 6 deletions
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11
kernel/trace/trace_syscalls.c
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@ -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 = {