Messages in this thread | | | Subject | Re: [PATCH] fs: fput() can be called from interrupt context | From | Trond Myklebust <> | Date | Sat, 14 Mar 2009 00:02:08 -0400 |
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On Fri, 2009-03-13 at 18:40 -0700, Davide Libenzi wrote: > On Fri, 13 Mar 2009, Trond Myklebust wrote: > > > On Thu, 2009-03-12 at 06:39 -0700, Davide Libenzi wrote: > > > On Wed, 11 Mar 2009, Andrew Morton wrote: > > > > > > > > Take the time to check how fs/aio.c handle the fput(req->ki_filp) case > > > > > (or read my 2nd patch, it should spot the thing) > > > > > > > > Well yes, a kludge like that seems a bit safer. > > > > > > > > It's somewhat encouraging that we're apparently already doing fput() > > > > from within keventd (although how frequently?). There might be > > > > problems with file locking, security code, etc from doing fput() from > > > > an unexpected thread. And then there are all the usual weird problem > > > > with using the keventd queues which take a long time to get discovered. > > > > > > Would it be a huge problem, performance-wise, to stop making ->f_count > > > tricks in __aio_put_req, and always offload to fput_work the task of > > > releasing the requests? > > > If that's a huge problem, IMO the lower impact fix would be to use > > > aio_fput_routine to loop into a second list, releasing the eventual > > > eventfd file*. There's no need, IMO, to turn the whole fput() into > > > IRQ-callable just for this case, when we can contain it into the > > > particular KAIO+eventfd usage. > > > > > > > Do you really want to see eventd doing umounts and remote flock() calls? > > This really needs to be run in a thread that can cope with __long__ > > waits, unavailable servers, etc... > > Did I miss something? This wouldn't be (eventually) on keventd shoulders, > but on aio work queue (aio_wq). > I guess we could do the same optimization we're already doing for ki_filp, > for ki_eventfd ...
Last I checked, a call to schedule_work(&fddef->wq) would still run fd_defer_queue() under keventd.
That said, even if you were to run it under aio_wq, the argument remains the same: do you really want to add potentially long lasting sleeps onto a work queue that was designed to service fast i/o requests?
Trond
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