From: Jens Axboe <axboe@kernel.dk>
To: Matthew Wilcox <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Benjamin LaHaise <bcrl@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Kees Cook <keescook@chromium.org>,
fsdevel <linux-fsdevel@vger.kernel.org>,
linux-aio@kvack.org, linux-mm <linux-mm@kvack.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Dan Carpenter <dan.carpenter@oracle.com>
Subject: Re: [PATCH] aio: Convert ioctx_table to XArray
Date: Tue, 11 Dec 2018 11:54:53 -0700 [thread overview]
Message-ID: <1629a25c-a9e7-e731-230d-e179e9f7a9a7@kernel.dk> (raw)
In-Reply-To: <20181211185311.GJ6830@bombadil.infradead.org>
On 12/11/18 11:53 AM, Matthew Wilcox wrote:
> 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.
They are not expensive, but they are not free either. And if we know we
are already under a rcu read lock, it seems pretty pointless. For the
two cases (memremap and aio), the rcu read lock is right there, before
the call. Easy to verify that it's safe.
--
Jens Axboe
next prev parent reply other threads:[~2018-12-11 18:54 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-28 18:35 [PATCH] aio: Convert ioctx_table to XArray Matthew Wilcox
2018-12-06 21:08 ` Matthew Wilcox
2018-12-06 22:21 ` Jeff Moyer
2018-12-06 22:26 ` Jeff Moyer
2018-12-11 17:21 ` Jeff Moyer
2018-12-11 17:51 ` Matthew Wilcox
2018-12-11 18:02 ` Jeff Moyer
2018-12-11 18:05 ` Jens Axboe
2018-12-11 18:09 ` Jeff Moyer
2018-12-11 18:37 ` Jens Axboe
2018-12-11 18:32 ` Jens Axboe
2018-12-11 18:36 ` Jens Axboe
2018-12-11 18:51 ` Matthew Wilcox
2018-12-11 18:52 ` Jens Axboe
2018-12-11 18:41 ` Jens Axboe
2018-12-11 18:45 ` Matthew Wilcox
2018-12-11 18:46 ` Jens Axboe
2018-12-11 18:53 ` Matthew Wilcox
2018-12-11 18:54 ` Jens Axboe [this message]
2018-12-11 18:53 ` Jens Axboe
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