linux-ext4 - Re: RFC: hold i_rwsem until aio completes

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Date:   Wed, 15 Jan 2020 20:07:44 +0100
From:   Christoph Hellwig <hch@....de>
To:     Waiman Long <longman@...hat.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Peter Zijlstra <peterz@...radead.org>,
        Christoph Hellwig <hch@....de>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-ext4@...r.kernel.org, cluster-devel@...hat.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: RFC: hold i_rwsem until aio completes

On Wed, Jan 15, 2020 at 02:03:22PM -0500, Waiman Long wrote:
> >> (1) no unlocking by another process than the one that acquired it
> >> (2) no return to userspace with locks held
> > As an example flow: obtain the read side lock, schedual a work queue,
> > return to user space, and unlock the read side from the work queue.
> 
> We currently have down_read_non_owner() and up_read_non_owner() that
> perform the lock and unlock without lockdep tracking. Of course, that is
> a hack and their use must be carefully scrutinized to make sure that
> there is no deadlock or other potentially locking issues.

That doesn't help with returning to userspace while the lock is held.