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Subject: Re: Memory uninitialized after "io_uring: keep table of pointers to
 ubufs"
To:     Andres Freund <andres@anarazel.de>
Cc:     Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20210529003350.m3bqhb3rnug7yby7@alap3.anarazel.de>
 <d2c5b250-5a0f-5de5-061f-38257216389d@gmail.com>
 <20210603180612.uchkn5qqa3j7rpgd@alap3.anarazel.de>
From:   Pavel Begunkov <asml.silence@gmail.com>
Message-ID: <9fa5c0f2-ff28-3775-9f4e-6a1cec06f151@gmail.com>
Date:   Fri, 4 Jun 2021 15:16:12 +0100
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On 6/3/21 7:06 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.

Yep, since you already narrowed it down. Thanks for testing

-- 
Pavel Begunkov