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Date:   Thu, 3 Jun 2021 11:06:12 -0700
From:   Andres Freund <andres@anarazel.de>
To:     Pavel Begunkov <asml.silence@gmail.com>
Cc:     Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: Memory uninitialized after "io_uring: keep table of pointers to
 ubufs"
Message-ID: <20210603180612.uchkn5qqa3j7rpgd@alap3.anarazel.de>
References: <20210529003350.m3bqhb3rnug7yby7@alap3.anarazel.de>
 <d2c5b250-5a0f-5de5-061f-38257216389d@gmail.com>
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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.

Greetings,

Andres Freund