Re: [fuse-devel] fuse: trying to steal weird page

[Nikolaus Rath <Nikolaus@rath.org>]

On Feb 26 2019, Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Tue, Feb 26, 2019 at 9:35 PM Nikolaus Rath <Nikolaus@rath.org> wrote:
>>
>> [ Moving fuse-devel and linux-fsdevel to Bcc ]
>>
>> Hello linux-mm people,
>>
>> I am posting this here as advised by Miklos (see below). In short, I
>> have a workload that reliably produces kernel messages of the form:
>>
>> [ 2562.773181] fuse: trying to steal weird page
>> [ 2562.773187] page=<something> index=<something> flags=17ffffc00000ad, count=1, mapcount=0, mapping= (null)
>>
>> What are the implications of this message? Is something activelly going
>> wrong (aka do I need to worry about data integrity)?
>
> Fuse is careful and basically just falls back on page copy, so it
> definitely shouldn't affect data integrity.
>
> The more interesting question is: how can page_cache_pipe_buf_steal()
> return a dirty page?  The logic in remove_mapping() should prevent
> that, but something is apparently slipping through...
>
>>
>> Is there something I can do to help debugging (and hopefully fixing)
>> this?
>>
>> This is with kernel 4.18 (from Ubuntu cosmic).
>
> One thought: have you tried reproducing with a recent vanilla
> (non-ubuntu) kernel?

Yes, I can reproduce with e.g. 5.0.0-050000rc8 (from
https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.0-rc8/). However, here
the flag value is different:

[  278.183571] fuse: trying to steal weird page
[  278.183576]   page=000000000aab208c index=14944 flags=17ffffc0000097, count=1, mapcount=0, mapping=          (null)

(but still the same across all messages observed with this kernel so
far).


Best,
-Nikolaus


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