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

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Message-ID: <d2c5b250-5a0f-5de5-061f-38257216389d@gmail.com>
Date:   Sat, 29 May 2021 12:03:12 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Andres Freund <andres@...razel.de>, Jens Axboe <axboe@...nel.dk>,
        io-uring@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Memory uninitialized after "io_uring: keep table of pointers to
 ubufs"

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.


> It only doesn't fail as root because the rlimit doesn't apply.
> 
> This is caused by
> 
> commit 41edf1a5ec967bf4bddedb83c48e02dfea8315b4
> Author: Pavel Begunkov <asml.silence@...il.com>
> Date:   2021-04-25 14:32:23 +0100
> 
>     io_uring: keep table of pointers to ubufs
> 
> Greetings,
> 
> Andres Freund
> 

-- 
Pavel Begunkov