[lkml]   [2018]   [Mar]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 07/30] aio: add delayed cancel support
On Thu, Mar 29, 2018 at 10:33:05PM +0200, Christoph Hellwig wrote:
> The upcoming aio poll support would like to be able to complete the
> iocb inline from the cancellation context, but that would cause a
> double lock of ctx_lock with the current locking scheme. Move the
> cancelation outside the context lock to avoid this reversal, which
> suits the existing usb gadgets users just fine as well (in fact
> both unconditionally disable irqs and thus seem broken without
> this change).
> To make this safe aio_complete needs to check if this call should
> complete the iocb. If it didn't the callers must not release any
> other resources.

Uh-oh... What happens to existing users of kiocb_set_cancel_fn() now?
AFAICS, those guys will *not* get aio_kiocb freed at all in case of
io_cancel(2). Look: we mark them with AIO_IOCB_CANCELLED and
call whatever ->ki_cancel() the driver has set. Later the damn
thing calls ->ki_complete() (i.e. aio_complete_rw()), which calls
aio_complete(iocb, res, res2, 0) and gets false. Nothing's freed,
struct file is leaked.

Frankly, the more I look at that, the less I like what you've done
with ->ki_cancel() overloading. In regular case it's just accelerating
the call of ->ki_complete(), which will do freeing. Here you have
->ki_cancel() free the damn thing, with the resulting need to play
silly buggers with locking, freeing logics in aio_complete(), etc.

 \ /
  Last update: 2018-03-30 00:36    [W:0.486 / U:0.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site