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Re: [RFC 0/3] block/file-posix: Work around XFS bug
From: |
Max Reitz |
Subject: |
Re: [RFC 0/3] block/file-posix: Work around XFS bug |
Date: |
Mon, 28 Oct 2019 10:24:02 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 |
On 27.10.19 13:35, Stefan Hajnoczi wrote:
> On Fri, Oct 25, 2019 at 11:58:46AM +0200, Max Reitz wrote:
>> As for how we can address the issue, I see three ways:
>> (1) The one presented in this series: On XFS with aio=native, we extend
>> tracked requests for post-EOF fallocate() calls (i.e., write-zero
>> operations) to reach until infinity (INT64_MAX in practice), mark
>> them serializing and wait for other conflicting requests.
>>
>> Advantages:
>> + Limits the impact to very specific cases
>> (And that means it wouldn’t hurt too much to keep this workaround
>> even when the XFS driver has been fixed)
>> + Works around the bug where it happens, namely in file-posix
>>
>> Disadvantages:
>> - A bit complex
>> - A bit of a layering violation (should file-posix have access to
>> tracked requests?)
>
> Your patch series is reasonable. I don't think it's too bad.
>
> The main question is how to detect the XFS fix once it ships. XFS
> already has a ton of ioctls, so maybe they don't mind adding a
> feature/quirk bit map ioctl for publishing information about bug fixes
> to userspace. I didn't see another obvious way of doing it, maybe a
> mount option that the kernel automatically sets and that gets reported
> to userspace?
I’ll add a note to the RH BZ.
> If we imagine that XFS will not provide a mechanism to detect the
> presence of the fix, then could we ask QEMU package maintainers to
> ./configure --disable-xfs-fallocate-beyond-eof-workaround at some point
> in the future when their distro has been shipping a fixed kernel for a
> while? It's ugly because it doesn't work if the user installs an older
> custom-built kernel on the host. But at least it will cover 98% of
> users...
:-/
I don’t like it, but I suppose it would work. We could also
automatically enable this disabling option in configure when we detect
uname to report a kernel version that must include the fix. (This
wouldn’t work for kernel with backported fixes, but those disappear over
time...)
Max
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- Re: [RFC 0/3] block/file-posix: Work around XFS bug, (continued)
Re: [RFC 0/3] block/file-posix: Work around XFS bug, no-reply, 2019/10/25
Re: [RFC 0/3] block/file-posix: Work around XFS bug, Nir Soffer, 2019/10/26
Re: [RFC 0/3] block/file-posix: Work around XFS bug, Stefan Hajnoczi, 2019/10/27
- Re: [RFC 0/3] block/file-posix: Work around XFS bug,
Max Reitz <=
- Re: [RFC 0/3] block/file-posix: Work around XFS bug, Max Reitz, 2019/10/28
- Re: [RFC 0/3] block/file-posix: Work around XFS bug, Max Reitz, 2019/10/28
- Re: [RFC 0/3] block/file-posix: Work around XFS bug, Vladimir Sementsov-Ogievskiy, 2019/10/28
- Re: [RFC 0/3] block/file-posix: Work around XFS bug, Max Reitz, 2019/10/28
- Re: [RFC 0/3] block/file-posix: Work around XFS bug, Vladimir Sementsov-Ogievskiy, 2019/10/28
Re: [RFC 0/3] block/file-posix: Work around XFS bug, Kevin Wolf, 2019/10/28