[for-next][PATCH 0/3] [3.16 and stable] tracing: Fixes to syscall tracing

[for-next][PATCH 0/3] [3.16 and stable] tracing: Fixes to syscall tracing

[Steven Rostedt]

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
for-next

Head SHA1: 72fa1a896d8ef355e81270667803ceb16a3dd13f


Oleg Nesterov (3):
      tracing: Fix syscall_*regfunc() vs copy_process() race
      tracing: Change syscall_*regfunc() to check PF_KTHREAD and use for_each_process_thread()
      tracing: syscall_regfunc() should not skip kernel threads

----
 include/trace/syscall.h | 15 +++++++++++++++
 kernel/fork.c           |  2 ++
 kernel/tracepoint.c     | 26 +++++++++++---------------
 3 files changed, 28 insertions(+), 15 deletions(-)

[for-next][PATCH 1/3] tracing: Fix syscall_*regfunc() vs copy_process() race

[Steven Rostedt]

[-- Attachment #1: 0001-tracing-Fix-syscall_-regfunc-vs-copy_process-race.patch --]
[-- Type: text/plain, Size: 2020 bytes --]

From: Oleg Nesterov <oleg@redhat.com>

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

Cc: stable@vger.kernel.org # 2.6.33
Fixes: a871bd33a6c0 "tracing: Add syscall tracepoints"
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/trace/syscall.h | 15 +++++++++++++++
 kernel/fork.c           |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/include/trace/syscall.h b/include/trace/syscall.h
index fed853f3d7aa..291c2824fafb 100644
--- 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>
 
@@ -32,4 +33,18 @@ struct syscall_metadata {
 	struct ftrace_event_call *exit_event;
 };
 
+#ifdef CONFIG_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 d2799d1fc952..6a13c46cd87d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1487,7 +1487,9 @@ 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)
-- 
2.0.0.rc2

[for-next][PATCH 2/3] tracing: Change syscall_*regfunc() to check PF_KTHREAD and use for_each_process_thread()

[Steven Rostedt]

[-- Attachment #1: 0002-tracing-Change-syscall_-regfunc-to-check-PF_KTHREAD-.patch --]
[-- Type: text/plain, Size: 2121 bytes --]

From: Oleg Nesterov <oleg@redhat.com>

1. Remove _irqsafe from syscall_regfunc/syscall_unregfunc,
   read_lock(tasklist) doesn't need to disable irqs.

2. Change this code to avoid the deprecated do_each_thread()
   and use for_each_process_thread() (stolen from the patch
   from Frederic).

3. Change syscall_regfunc() to check PF_KTHREAD to skip
   the kernel threads, ->mm != NULL is the common mistake.

   Note: probably this check should be simply removed, needs
   another patch.

[fweisbec@gmail.com: s/do_each_thread/for_each_process_thread/]
Link: http://lkml.kernel.org/p/20140413185918.GC20668@redhat.com

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/tracepoint.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 33cbd8c203f8..9cf12640de5a 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -492,33 +492,31 @@ static int sys_tracepoint_refcount;
 
 void syscall_regfunc(void)
 {
-	unsigned long flags;
-	struct task_struct *g, *t;
+	struct task_struct *p, *t;
 
 	if (!sys_tracepoint_refcount) {
-		read_lock_irqsave(&tasklist_lock, flags);
-		do_each_thread(g, t) {
+		read_lock(&tasklist_lock);
+		for_each_process_thread(p, t) {
 			/* Skip kernel threads. */
-			if (t->mm)
+			if (!(t->flags & PF_KTHREAD))
 				set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
-		} while_each_thread(g, t);
-		read_unlock_irqrestore(&tasklist_lock, flags);
+		}
+		read_unlock(&tasklist_lock);
 	}
 	sys_tracepoint_refcount++;
 }
 
 void syscall_unregfunc(void)
 {
-	unsigned long flags;
-	struct task_struct *g, *t;
+	struct task_struct *p, *t;
 
 	sys_tracepoint_refcount--;
 	if (!sys_tracepoint_refcount) {
-		read_lock_irqsave(&tasklist_lock, flags);
-		do_each_thread(g, t) {
+		read_lock(&tasklist_lock);
+		for_each_process_thread(p, t) {
 			clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
-		} while_each_thread(g, t);
-		read_unlock_irqrestore(&tasklist_lock, flags);
+		}
+		read_unlock(&tasklist_lock);
 	}
 }
 #endif
-- 
2.0.0.rc2

[for-next][PATCH 3/3] tracing: syscall_regfunc() should not skip kernel threads

[Steven Rostedt]

[-- Attachment #1: 0003-tracing-syscall_regfunc-should-not-skip-kernel-threa.patch --]
[-- Type: text/plain, Size: 1552 bytes --]

From: Oleg Nesterov <oleg@redhat.com>

syscall_regfunc() ignores the kernel threads because "it has no effect",
see cc3b13c1 "Don't trace kernel thread syscalls" which added this check.

However, this means that a user-space task spawned by call_usermodehelper()
will run without TIF_SYSCALL_TRACEPOINT if sys_tracepoint_refcount != 0.

Remove this check. The unnecessary report from ret_from_fork path mentioned
by cc3b13c1 is no longer possible, see See commit fb45550d76bb5 "make sure
that kernel_thread() callbacks call do_exit() themselves".

A kernel_thread() callback can only return and take the int_ret_from_sys_call
path after do_execve() succeeds, otherwise the kernel will crash. But in this
case it is no longer a kernel thread and thus is needs TIF_SYSCALL_TRACEPOINT.

Link: http://lkml.kernel.org/p/20140413185938.GD20668@redhat.com

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/tracepoint.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 9cf12640de5a..3490407dc7b7 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -497,9 +497,7 @@ void syscall_regfunc(void)
 	if (!sys_tracepoint_refcount) {
 		read_lock(&tasklist_lock);
 		for_each_process_thread(p, t) {
-			/* Skip kernel threads. */
-			if (!(t->flags & PF_KTHREAD))
-				set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
+			set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
 		}
 		read_unlock(&tasklist_lock);
 	}
-- 
2.0.0.rc2