On Sun, 2013-03-17 at 19:28 +0100, Oleg Nesterov 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.
Is this because "p = dup_task_struct(current);" is outside the lock?
Probably should state this in the change log.
>
> While at it,
>
> - remove _irqsafe from syscall_regfunc/syscall_unregfunc,
> read_lock(tasklist) doesn't need to disable irqs.
I'm fine with this.
>
> - change syscall_unregfunc() to check PF_KTHREAD to skip
> the kernel threads, ->mm != NULL is the common mistake.
I'm fine with this too.
>
> Note: probably this check should be simply removed, needs
> another patch.
>
> Signed-off-by: Oleg Nesterov <o...@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 1766d32..8184a53 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1472,7 +1472,14 @@ static struct task_struct *copy_process(unsigned long
> clone_flags,
>
> total_forks++;
> spin_unlock(¤t->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
I hate seeing #ifdef code like this in C files. Can you add a function
to set this in include/trace/syscalls.h:
#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
Then in copy_process() just have:
syscall_tracepoint_update(p);
Thanks,
-- Steve
> 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 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);
> }
> }
> #endif
--
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