linux-kernel - Re: [PATCH] iomap: Fix the write_count in iomap_add_to

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200821060025.GA31091@infradead.org>
Date:   Fri, 21 Aug 2020 07:00:25 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     Dave Chinner <david@...morbit.com>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>, hch@...radead.org,
        darrick.wong@...cle.com, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        willy@...radead.org
Subject: Re: [PATCH] iomap: Fix the write_count in iomap_add_to_ioend().

On Fri, Aug 21, 2020 at 10:15:33AM +0530, Ritesh Harjani wrote:
> Please correct me here, but as I see, bio has only these two limits
> which it checks for adding page to bio. It doesn't check for limits
> of /sys/block/<dev>/queue/* no? I guess then it could be checked
> by block layer below b4 submitting the bio?

The bio does not, but the blk-mq code will split the bios when mapping
it to requests, take a look at blk_mq_submit_bio and __blk_queue_split.

But while the default limits are quite low, they can be increased
siginificantly, which tends to help with performance and is often
also done by scripts shipped by the distributions.

> This issue was first observed while running a fio run on a system with
> huge memory. But then here is an easy way we figured out to trigger the
> issue almost everytime with loop device on my VM setup. I have provided
> all the details on this below.

Can you wire this up for xfstests?