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Re: multifd/tcp/zlib intermittent abort

From: Thomas Huth
Subject: Re: multifd/tcp/zlib intermittent abort
Date: Tue, 15 Mar 2022 16:44:37 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.0

On 15/03/2022 16.40, Daniel P. Berrangé wrote:
On Tue, Mar 15, 2022 at 03:30:27PM +0000, Peter Maydell wrote:
On Tue, 15 Mar 2022 at 15:03, Peter Maydell <peter.maydell@linaro.org> wrote:
Maybe we're running into this bug
("zlib: compressBound() returns an incorrect result on z15") ?

Full repro info, since it's a bit hidden in this long thread:

Build an i386 guest QEMU; I used this configure command:

'../../configure' '--target-list=i386-softmmu' '--enable-debug'
'--with-pkgversion=pm215' '--disable-docs'

Then run the multifd/tcp/zlib test in a tight loop:

X=1; while QTEST_QEMU_BINARY=./build/i386/i386-softmmu/qemu-system-i386
./build/i386/tests/qtest/migration-test  -tap -k -p
/i386/migration/multifd/tcp/zlib ; do echo $X; X=$((X+1)); done

Without DFLTCC=0 it fails typically within 5 or so iterations;
the longest I've ever seen it go is about 32.

So if this is a host OS package bug we punt to OS vendor to fix,
and just apply workaround in our CI ?  eg

$ git diff
diff --git a/.travis.yml b/.travis.yml
index c3c8048842..6da4c9f640 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -218,6 +218,7 @@ jobs:
          - TEST_CMD="make check check-tcg V=1"
          - CONFIG="--disable-containers 
          - UNRELIABLE=true
+        - DFLTCC=0
          - BUILD_RC=0 && make -j${JOBS} || BUILD_RC=$?
          - |

Sounds like a good idea - but you should certainly add a proper comment here, too, so that we can later remind ourselves to remove the workaround again.


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