[for-next][PATCH v2 0/3] tracing: Fixes to syscall tracing

[for-next][PATCH v2 0/3] tracing: Fixes to syscall tracing

[Steven Rostedt]

I don't like to do this but I rebased my for-next branch to have
the first (for stable) patch not break other archs. This set passed my
cross compile test as well as my normal tests.

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

Head SHA1: 0f6af1fe54b371ab6dfc05d963c0356a43c83226


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 v2 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: 2066 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..9674145e2f6a 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;
 };
 
+#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 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

[for-next][PATCH v2 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: 2117 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

[for-next][PATCH v2 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: 1548 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

Re: [for-next][PATCH v2 1/3] tracing: Fix syscall_*regfunc() vs copy_process() race

[Paul E. McKenney]

On Fri, Jun 20, 2014 at 06:45:19AM -0400, Steven Rostedt wrote:
> 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>

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
>  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..9674145e2f6a 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;
>  };
>  
> +#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 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
> 
> 
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Re: [for-next][PATCH v2 1/3] tracing: Fix syscall_*regfunc() vs copy_process() race

[Steven Rostedt]

On Fri, 20 Jun 2014 18:11:25 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> On Fri, Jun 20, 2014 at 06:45:19AM -0400, Steven Rostedt wrote:
> > 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>
> 
> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 

I don't usually rebase my for-next branch for acks, but I already
rebased once for fixing an issue, and it's early in the rc cycle, and
this is the first patch on the branch, so I think I will do it.

Thanks!

-- Steve

Re: [for-next][PATCH v2 1/3] tracing: Fix syscall_*regfunc() vs copy_process() race

[Namhyung Kim]

Hi Steve,

On Fri, 20 Jun 2014 06:45:19 -0400, Steven Rostedt wrote:
> 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.

s/tasklist/tasklist_lock/ ?

Probably I'm too late..

Thanks,
Namhyung

Re: [for-next][PATCH v2 1/3] tracing: Fix syscall_*regfunc() vs copy_process() race

[Steven Rostedt]

On Tue, 24 Jun 2014 15:55:41 +0900
Namhyung Kim <namhyung@kernel.org> wrote:

> Hi Steve,
> 
> On Fri, 20 Jun 2014 06:45:19 -0400, Steven Rostedt wrote:
> > 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.
> 
> s/tasklist/tasklist_lock/ ?
> 
> Probably I'm too late..

Yeah, but it's just a change log, and I think people can figure it out
(I hope).

-- Steve