linux-kernel - Re: io_pgetevents & aio fsync V2

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Message-ID: <20180406062700.GA20714@lst.de>
Date:   Fri, 6 Apr 2018 08:27:00 +0200
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Christoph Hellwig <hch@....de>, Avi Kivity <avi@...lladb.com>,
        linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: io_pgetevents & aio fsync V2

On Fri, Apr 06, 2018 at 04:16:30AM +0100, Al Viro wrote:
> BTW, this is only tangentially related, but... does *anything* call
> io_submit() for huge amounts of iocb?  Check in do_io_submit() is
> insane - "no more than MAX_LONG total of _pointers_".  Compat variant
> goes for "no more than a page worth of pointers" and there's
> a hard limit in ioctx_alloc() - we can't ever get more than
> 8M slots in ring buffer...

Logical upper bound for io_submit is nr_events passed to io_setup(),
which is bound by aio_max_nr.  Except that we never actually check
against nr_events (or max_reqs as it is known in kernel) in io_submit.
Sigh..