RE: [PATCH] io_uring: fix iovec leaks

[David Laight <David.Laight@ACULAB.COM>]

From: Pavel Begunkov
> Sent: 11 February 2020 11:05
> On 2/11/2020 1:07 PM, David Laight wrote:
> > From: Pavel Begunkov
> >> Sent: 07 February 2020 19:05
> >> Allocated iovec is freed only in io_{read,write,send,recv)(), and just
> >> leaves it if an error occured. There are plenty of such cases:
> >> - cancellation of non-head requests
> >> - fail grabbing files in __io_queue_sqe()
> >> - set REQ_F_NOWAIT and returning in __io_queue_sqe()
> >> - etc.
> >>
> >> Add REQ_F_NEED_CLEANUP, which will force such requests with custom
> >> allocated resourses go through cleanup handlers on put.
> >
> > This looks horribly fragile.
> 
> Well, not as horrible as it may appear -- set the flag, whenever you
> want the corresponding destructor to be called, and clear it when is not
> needed anymore.
> 
> I'd love to have something better, maybe even something more intrusive
> for-next, but that shouldn't hurt the hot path. Any ideas?

Given all the 'cud chewing' that happens in code paths
like the one that read iov from userspace just adding:

	if (unlikely(foo->ptr))
		kfree(foo->ptr);

before 'foo' goes out of scope (or is reused) is probably
not measurable.

	David

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