Messages in this thread | | | From | Linus Torvalds <> | Date | Sun, 14 Nov 2021 11:02:31 -0800 | Subject | Re: [GIT pull] timers/urgent for v5.16-rc1 |
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On Sun, Nov 14, 2021 at 5:31 AM Thomas Gleixner <tglx@linutronix.de> wrote: > > + /* > + * A copied work entry from the old task is not meaningful, clear it. > + * N.B. init_task_work will not do this. > + */ > + memset(&p->posix_cputimers_work.work, 0, > + sizeof(p->posix_cputimers_work.work)); > + init_task_work(&p->posix_cputimers_work.work, > + posix_cpu_timers_work);
Ugh.
Instead of the added four lines of comment, and two lines of "memset()", maybe this should just have made init_task_work() DTRT?
Yes,. I see this:
/* Protect against double add, see task_tick_numa and task_numa_work */ p->numa_work.next = &p->numa_work; ... init_task_work(&p->numa_work, task_numa_work);
but I think that one is so subtle and such a special case that it should have been updated - just make that magic special flag happen after the init_task_work.
A lot of the other cases seem to zero-initialize things elsewhere (generally with kzalloc()), but I note that at least io_ring_exit_work() seems to have this:
struct io_tctx_exit exit; ... init_task_work(&exit.task_work, io_tctx_exit_cb);
and the ->next pointer is never set to NULL.
Now, in 99% of all cases the ->next pointer simply doesn't matter, because task_work_add() will only set it, not caring about the old value.
But apparently it matters for posix_cputimers_work and for numa_work, and so I think it's very illogical that init_task_work() will not actually initialize it properly.
Hmm?
I've pulled this, but it really looks like the wrong solution to the whole "uninitialized data".
And that task_tick_numa() special case is truly horrendous, and really should go after the init_task_work() regardless, exactly because you'd expect that init_task_work() to initialize the work even if it doesn't happen to right now.
Or is somebody doing init_task_work() to only change the work-function on an already initialized work entry? Becuase that sounds both racy and broken to me, and none of the things I looked at from a quick grep looked like that at all.
Linus
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