[CRIU] BUG: CRIU corrupt floating point state after checkpoint

[Diyu Zhou]

Hey CRIU,

It seems to me that CRIU corrupts the floating point of the process after
checkpointing. I was wondering if I did something wrong with CRIU or it is a
bug.

To illustrate it, I wrote a simple floating point program that keeps
calculating the average value of three floating point array elements. I use
CRIU to checkpoint it as follows:

$criu dump -t pid --leave-running --shell-job

After several iterations, I can observe that some of the floating point
registers are modified to 0 and causes the program to output incorrect result.

One thing I have observed is that the floating point corruption does not occur
on the main thread but only on other threads.

I have attached my /proc/cpuinfo output, the dump log of CRIU and the
simple benchmark I have used to illustrate the program (please run it with
./ftress1 8 1000 1), together with a bash script I wrote to invoke CRIU to
checkpoint the program constantly.

I'm on an x86 machine installed with Fedora 29, Kernel version: 4.20.13.  The
version of CRIU is shown below (just downloaded from github)

$criu -v

Version: 3.12
GitID: v3.12-259-g4d7f74aa
Thank you for your help and I'm happy to provide more information.

Best,
Diyu
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