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Subject[PATCH 1/2] tracing: syscall_*regfunc() can race with copy_process()
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
init_task.tasks list yet.

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

While at it,

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

- change syscall_unregfunc() 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.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/fork.c | 7 +++++++
kernel/tracepoint.c | 12 +++++-------
2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 34d7ed1..772d4a5 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1446,7 +1446,14 @@ static struct task_struct *copy_process(unsigned long clone_flags,

total_forks++;
spin_unlock(&current->sighand->siglock);
+#ifdef CONFIG_TRACEPOINTS
+ if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+ set_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT);
+ else
+ clear_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT);
+#endif
write_unlock_irq(&tasklist_lock);
+
proc_fork_connector(p);
cgroup_post_fork(p);
if (clone_flags & CLONE_THREAD)
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index f1539de..e2a4523 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -734,33 +734,31 @@ static int sys_tracepoint_refcount;

void syscall_regfunc(void)
{
- unsigned long flags;
struct task_struct *g, *t;

if (!sys_tracepoint_refcount) {
- read_lock_irqsave(&tasklist_lock, flags);
+ read_lock(&tasklist_lock);
do_each_thread(g, 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;

sys_tracepoint_refcount--;
if (!sys_tracepoint_refcount) {
- read_lock_irqsave(&tasklist_lock, flags);
+ read_lock(&tasklist_lock);
do_each_thread(g, 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
--
1.5.5.1



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