On Wed, 9 Apr 2014 19:05:42 +0200
Oleg Nesterov <o...@redhat.com> wrote:
> 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 <o...@redhat.com>
> ---
> include/trace/syscall.h | 15 +++++++++++++++
> kernel/fork.c | 2 ++
> kernel/tracepoint.c | 12 +++++-------
> 3 files changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/include/trace/syscall.h b/include/trace/syscall.h
> index 84bc419..15a954b 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>
>
> @@ -31,4 +32,18 @@ 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 1766d32..e463f99 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1472,7 +1472,9 @@ static struct task_struct *copy_process(unsigned long
> clone_flags,
>
> total_forks++;
> spin_unlock(¤t->sighand->siglock);
> + syscall_tracepoint_update(p);
> write_unlock_irq(&tasklist_lock);
> +
So this looks to be a fix that probably should go to stable?
> proc_fork_connector(p);
> cgroup_post_fork(p);
> if (clone_flags & CLONE_THREAD)
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 0c05a45..a16754b 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -732,33 +732,31 @@ 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);
These changes should be in a separate patch, as they can wait till 3.16.
-- Steve
> }
> }
> #endif
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