Messages in this thread | | | From | Linus Torvalds <> | Date | Wed, 18 Aug 2021 19:57:32 -0700 | Subject | Re: [PATCH] kernel: make TIF_NOTIFY_SIGNAL and core dumps co-exist |
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On Tue, Aug 17, 2021 at 8:06 PM Jens Axboe <axboe@kernel.dk> wrote: > > task_work being added with notify == TWA_SIGNAL will utilize > TIF_NOTIFY_SIGNAL for signaling the targeted task that work is available. > If this happens while a task is going through a core dump, it'll > potentially disturb and truncate the dump as a signal interruption.
This patch seems (a) buggy and (b) hacky.
> --- a/kernel/task_work.c > +++ b/kernel/task_work.c > @@ -41,6 +41,12 @@ int task_work_add(struct task_struct *task, struct callback_head *work, > head = READ_ONCE(task->task_works); > if (unlikely(head == &work_exited)) > return -ESRCH; > + /* > + * TIF_NOTIFY_SIGNAL notifications will interfere with > + * a core dump in progress, reject them. > + */ > + if (notify == TWA_SIGNAL && (task->flags & PF_SIGNALED)) > + return -ESRCH;
This basically seems to check task->flags with no serialization.
I'm sure it works 99.9% of the time in practice, since you'd be really unlucky to hit any races, but I really don't see what the serialization logic is.
Also, the main user that actually triggered the problem already has
if (unlikely(tsk->flags & PF_EXITING)) goto fail;
just above the call to task_work_add(), so this all seems very hacky indeed.
Of course, I don't see what the serialization for _that_ one is either.
Pls explain. You can't just randomly add tests for random flags that get modified by other random code.
Linus
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