potential riscv special bug maybe found

[Alexandre Ghiti]

Hi Aurélien, Bo,


On 09/08/2023 16:47, Aurelien Jarno wrote:
> Hi,
>
> On 2023-03-09 23:18, Bo YU wrote:
>> Hi,
>>
>> I am sorry if this is noise.
>>
>> Some days ago I noticed strace 6.2 was built failed on riscv64 due to
>> test cases[0]. There is one program from strace can reproduce it:
>>
>> ```
>> ./tests/read-write ```
>>
>> It will be hang.
>>
>> In fact, the issue has existed since 5.18. I `git bisect` and finally
>> found out the issue was introduced by the commit[1]:
>>
>> commit 631f871f071746789e9242e514ab0f49067fa97a
>> Author: Andreas Gruenbacher <agruenba at redhat.com>
>> Date:   Tue Nov 9 12:56:06 2021 +0100
>>
>>      fs/iomap: Fix buffered write page prefaulting
>>
>> I do not think there is a problem with this commit, because it does not
>> affect others arch expect riscv and after I reverted it, it will pass
>> all test cases from strace(There is still one case failed on qemu, but
>> this is another store).
>>
>> I try to debug something but failed.
>> Would be appreciated it any help.
> Please find attached a simpler reproducer extracted from strace, which
> should make the issue easier to reproduce. It hangs on riscv64 and needs
> to be killed with -9, while it works fine on amd64.


Thanks for the reproducer, I was able to reproduce the problem: the 
kernel is stuck trying to copy data from user, I'm looking into it right 
now as this seems very weird. Note that I will be on vacation at the end 
of the week, if I don't have time to fix this, I'll post my findings here.


Thanks again,

Alex


> Regards
> Aurelien
>
>
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