bug#40527: qemu 4.2.0 test suite hangs on i686-linux

[Ludovic Courtès]

The test suite of QEMU 4.2.0 systematically hangs on i686-linux:

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MALLOC_PERTURB_=${MALLOC_PERTURB_:-$(( ${RANDOM:-0} % 255 + 1))}  
QTEST_QEMU_BINARY=i386-softmmu/qemu-system-i386 QTEST_QEMU_IMG=qemu-img 
tests/migration-test -m=quick -k --tap < /dev/null | ./scripts/tap-driver.pl 
--test-name="migration-test" 
PASS 1 migration-test /i386/migration/deprecated
PASS 2 migration-test /i386/migration/bad_dest
PASS 3 migration-test /i386/migration/fd_proto
PASS 4 migration-test /i386/migration/validate_uuid
PASS 5 migration-test /i386/migration/validate_uuid_error
PASS 6 migration-test /i386/migration/validate_uuid_src_not_set
PASS 7 migration-test /i386/migration/validate_uuid_dst_not_set
building of 
`/gnu/store/3k4ncd7d41va4kflila981246ai83xzi-qemu-minimal-4.2.0.drv' timed out 
after 3600 seconds of silence
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The process tree at that point looks like this:

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$ pstree -p |grep  -A50 8930
            |-guix-daemon(32573)-+-guix-daemon(8165)-+-guile(8930)-+-117(1351)
            |                    |                   |             |-117(1375)
            |                    |                   |             |-117(1405)
            |                    |                   |             |-117(1443)
            |                    |                   |             |-117(1477)
            |                    |                   |             |-117(1516)
            |                    |                   |             |-117(1534)
            |                    |                   |             |-117(1559)
            |                    |                   |             |-140(2420)
            |                    |                   |             |-140(2445)
            |                    |                   |             |-140(2468)
            |                    |                   |             |-140(2491)
            |                    |                   |             |-140(2522)
            |                    |                   |             |-140(2553)
            |                    |                   |             |-141(2630)
            |                    |                   |             |-141(2654)
            |                    |                   |             |-141(2678)
            |                    |                   |             |-141(2706)
            |                    |                   |             |-141(2724)
            |                    |                   |             |-141(2742)
            |                    |                   |             |-141(2760)
            |                    |                   |             |-141(2788)
            |                    |                   |             |-141(2811)
            |                    |                   |             |-141(2829)
            |                    |                   |             |-141(2847)
            |                    |                   |             |-141(2865)
            |                    |                   |             |-141(2883)
            |                    |                   |             |-141(2906)
[…]
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Ludo’.