tracing: Fix syscall_*regfunc() vs copy_process() race

commit 4af4206be2bd1933cae20c2b6fb2058dbc887f7c upstream.

syscall_regfunc() and syscall_unregfunc() should set/clear
TIF_SYSCALL_TRACEPOINT system-wide, but do_each_thread() can race
with copy_process() and miss the new child which was not added to
the process/thread lists yet.

Change copy_process() to update the child's TIF_SYSCALL_TRACEPOINT
under tasklist.

Link: http://lkml.kernel.org/p/20140413185854.GB20668@redhat.com
Fixes: a871bd33a6c0 "tracing: Add syscall tracepoints"
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/trace/syscall.h b/include/trace/syscall.h
index 84bc4197e73659c3ff48967e7710fbf5fb549c36..0a5b4952aa30b1919d4d2297cde0f05998dbb64a 100644 (file)
--- a/include/trace/syscall.h
+++ b/include/trace/syscall.h
@@ -4,6 +4,7 @@
 #include <linux/tracepoint.h>
 #include <linux/unistd.h>
 #include <linux/ftrace_event.h>
+#include <linux/thread_info.h>
 
 #include <asm/ptrace.h>
 
@@ -31,4 +32,18 @@ struct syscall_metadata {
        struct ftrace_event_call *exit_event;
 };
 
+#if defined(CONFIG_TRACEPOINTS) && defined(CONFIG_HAVE_SYSCALL_TRACEPOINTS)
+static inline void syscall_tracepoint_update(struct task_struct *p)
+{
+       if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+               set_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT);
+       else
+               clear_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT);
+}
+#else
+static inline void syscall_tracepoint_update(struct task_struct *p)
+{
+}
+#endif
+
 #endif /* _TRACE_SYSCALL_H */

diff --git a/kernel/fork.c b/kernel/fork.c
index 270c1dab674a59df3ea52c48e05ad9cca5246166..814363a69b80142822e20990eced1c7f1fe20215 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1479,7 +1479,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 
        total_forks++;
        spin_unlock(&current->sighand->siglock);
+       syscall_tracepoint_update(p);
        write_unlock_irq(&tasklist_lock);
+
        proc_fork_connector(p);
        cgroup_post_fork(p);
        if (clone_flags & CLONE_THREAD)