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SubjectRe: [PATCH 09/11] job control: reorganize wait_task_stopped()
On 05/08, Tejun Heo wrote:
>
> wait_task_stopped() tested task_stopped_code() without acquiring
> siglock and, if stop condition existed, called wait_task_stopped() and
> directly returned the result.
>
> it may race against SIGCONT generation.

Hmm. This is the plain bug, even if unlikely and minor.

> It seems that WNOHANG wait correctness has never been guaranteed and
> everybody has been happy with it for very long time.

Yes, the window is tiny. May be it was never noticed or never
reported because this is hard to diagnose/reproduced.

> As such,
> although this reorganization improves the situation a bit, I don't
> consider this to be a bug fix.

But it is?

Can't we push this patch ahead of these changes? I can merge it into
ptrace branch.


> static int wait_task_stopped(struct wait_opts *wo,
> int ptrace, struct task_struct *p)
> @@ -1397,6 +1409,9 @@ static int wait_task_stopped(struct wait_opts *wo,
> if (!ptrace && !(wo->wo_flags & WUNTRACED))
> return 0;
>
> + if (!task_stopped_code(p, ptrace))
> + return 0;
> +
> exit_code = 0;
> spin_lock_irq(&p->sighand->siglock);
>
> @@ -1607,8 +1622,9 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
> * Wait for stopped. Depending on @ptrace, different stopped state
> * is used and the two don't interact with each other.
> */
> - if (task_stopped_code(p, ptrace))
> - return wait_task_stopped(wo, ptrace, p);
> + ret = wait_task_stopped(wo, ptrace, p);
> + if (ret)
> + return ret;

Reviewed-by: Oleg Nesterov <oleg@redhat.com>



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