linux-kernel - Re: [PATCH] aio: Convert ioctx

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Message-ID: <20181211185311.GJ6830@bombadil.infradead.org>
Date:   Tue, 11 Dec 2018 10:53:11 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Benjamin LaHaise <bcrl@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        fsdevel <linux-fsdevel@...r.kernel.org>, linux-aio@...ck.org,
        linux-mm <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] aio: Convert ioctx_table to XArray

On Tue, Dec 11, 2018 at 11:46:53AM -0700, Jens Axboe wrote:
> On 12/11/18 11:45 AM, Matthew Wilcox wrote:
> > I think we need the rcu read lock here to prevent ctx from being freed
> > under us by free_ioctx().
> 
> Then that begs the question, how about __xa_load() that is already called
> under RCU read lock?

I've been considering adding it to the API, yes.  I was under the
impression that nested rcu_read_lock() calls were not expensive, even
with CONFIG_PREEMPT.