linux-kernel - Re: Memory uninitialized after "io_uring: keep table of pointers to ubufs"

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Date:   Thu, 3 Jun 2021 12:13:52 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Andres Freund <andres@...razel.de>,
        Pavel Begunkov <asml.silence@...il.com>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Memory uninitialized after "io_uring: keep table of pointers to
 ubufs"

On 6/3/21 12:06 PM, Andres Freund wrote:
> Hi,
> 
> On 2021-05-29 12:03:12 +0100, Pavel Begunkov wrote:
>> On 5/29/21 1:33 AM, Andres Freund wrote:
>>> Hi,
>>>
>>> I started to see buffer registration randomly failing with ENOMEM on
>>> 5.13. Registering buffer or two often succeeds, but more than that
>>> rarely. Running the same program as root succeeds - but the user has a high
>>> rlimit.
>>>
>>> The issue is that io_sqe_buffer_register() doesn't initialize
>>> imu. io_buffer_account_pin() does imu->acct_pages++, before calling
>>> io_account_mem(ctx, imu->acct_pages);
>>>
>>> Which means that a random amount of memory is being accounted for. On the first
>>> few allocations this sometimes fails to fail because the memory is zero, but
>>> after a bit of reuse...
>>
>> Makes sense, thanks for digging in. I've just sent a patch, would
>> be great if you can test it or send your own.
> 
> Sorry for the slow response, I'm off this week. I did just get around to
> test and unsurprisingly: The patch does fix the issue.

OK good, thanks for confirming, I did ship it out earlier today so
should be in the next -rc.

-- 
Jens Axboe