Messages in this thread | | | Subject | Re: deferring __fput() | From | Peter Zijlstra <> | Date | Mon, 25 Jun 2012 15:19:56 +0200 |
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On Mon, 2012-06-25 at 13:14 +0100, Al Viro wrote:
> You mean, doing that from RCU callbacks?
Indirectly, yeah, but the RCU callback would schedule it or whatever.
> Still a bad idea, IMO; you will end up with a context > switch and unpleasantness with delayed user-visible effects of syscalls. With aio we did have > a delayed execution of fput() anyway; all that has changed there is that we use generic > mechanism instead of home-grown analog thereof.
Right, the delayed effect is the main concern. The example in the referred thread was unmount() returning -EBUSY after the last close()/munmap().
> I'll need to reread that thread to comment on the specifics (had been too long ago; I don't > remember the details), but... See Linus' objections to full-async fput() circa this April > or March. There's a reason why this patchset uses task_work_add() whenever possible.
Ok, I'll try and find that thread, so the advantage of task_work_add() is that you'll keep the work in the task that caused it wherever possible, right -- provided its actually sitll around.
If we make fput() deferable in general we'll be sure to grow some 'fun' cases. So are we going to add a sync against unmount someplace to avoid these un-expected -EBUSY things?
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