[Samba] io_uring cause data corruption

[Jeremy Allison]

On Mon, Apr 27, 2020 at 11:21:35PM +0200, A L wrote:
> 
> I set up the following test case:
> * Linux 5.7-rc3 (with the patch from previous mail)
> * samba-4.12.1
> * gcc-9.3.0
> * liburing-0.6
> * glibc-2.30-r8
> 
> =================================
> Test 1)
> Copy 10 10GB files.
> 1) ddrescue -s 10G -v -f /dev/urandom 0.bin
> 2) for((i=1;i<=10;i+=1)); do cp --reflink=always 0.bin $i.bin; done
> 3) sha256sum *.bin > sha256sum.txt
> 4) Windows 10, file explorer, copy the 10 files to a local disk D:\test\
> 5) Verify local files in D:\test with sha256sum
> 6) sha256sum was correct.
> 7) redid step 4 and 5. Now sha256sum was wrong, but all 10 files had the
> same (but wrong) csum!
> 
> 
> =================================
> Test 2)
> Copy 1000 10MB files.
> 1) ddrescue -s 10M -v -f /dev/urandom 0.bin
> 2) for((i=1;i<=1000;i+=1)); do cp --reflink=always 0.bin $i.bin; done
> 3) sha256sum *.bin > sha256sum.txt
> 4) Windows 10, file explorer, copy all 1000 files to a local disk D:\test\
> 5) Verify local files in D:\test with sha256sum

I just tried to reproduce this using
Samba master on Ubuntu 19.10 kernel 5.3.0-51-generic
liburing-dev:0.4-2.

I only tried with 100 files, and fetched
them using smbclient "mget", and the results
were always the same - identical sha256sum
hashes on all files.

We're going to need more info to track this
down in your environment I'm afraid.