tests/basic/quick-read-with-upcall.t is flaky

[mykaul]

          It inconsistently fails on my laptop, so I assume there's something not working well yet:

[ykaul@ykaul glusterfs]$ sudo prove -vf tests/basic/quick-read-with-upcall.t 
tests/basic/quick-read-with-upcall.t .. 
1..33
losetup: /d/dev/loop*: failed to use device: No such device
ok   1 [    234/    901] <   9> 'glusterd'
ok   2 [     15/      8] <  10> 'pidof glusterd'
No volumes present
ok   3 [      8/     41] <  11> 'gluster --mode=script --wignore volume info'
ok   4 [      6/    176] <  14> 'gluster --mode=script --wignore volume create patchy 10.100.102.15:/d/backends/patchy1 10.100.102.15:/d/backends/patchy2'
ok   5 [     12/    224] <  15> 'gluster --mode=script --wignore volume start patchy'
ok   6 [      7/     15] <  18> 'glusterfs -s 10.100.102.15 --volfile-id patchy --direct-io-mode=enable /mnt/glusterfs/0'
ok   7 [      7/     15] <  19> 'glusterfs -s 10.100.102.15 --volfile-id patchy --direct-io-mode=enable /mnt/glusterfs/1'
ok   8 [      8/      2] <  32> 'write_to /mnt/glusterfs/0/test.txt test-message0'
ok   9 [      7/      2] <  33> 'test-message0 cat /mnt/glusterfs/0/test.txt'
ok  10 [      6/      2] <  34> 'test-message0 cat /mnt/glusterfs/1/test.txt'
ok  11 [      7/      1] <  36> 'write_to /mnt/glusterfs/0/test.txt test-message1'
ok  12 [      7/      2] <  37> 'test-message1 cat /mnt/glusterfs/0/test.txt'
ok  13 [      7/      2] <  38> 'test-message0 cat /mnt/glusterfs/1/test.txt'
ok  14 [   1014/      7] <  43> 'test-message1 cat /mnt/glusterfs/1/test.txt'
ok  15 [     13/    122] <  45> 'gluster --mode=script --wignore volume set patchy features.cache-invalidation on'
ok  16 [     15/    110] <  46> 'gluster --mode=script --wignore volume set patchy performance.quick-read-cache-timeout 15'
ok  17 [     10/    115] <  47> 'gluster --mode=script --wignore volume set patchy performance.md-cache-timeout 15'
ok  18 [     14/      3] <  49> 'write_to /mnt/glusterfs/0/test1.txt test-message0'
ok  19 [      9/      2] <  50> 'test-message0 cat /mnt/glusterfs/0/test1.txt'
ok  20 [      7/      3] <  51> 'test-message0 cat /mnt/glusterfs/1/test1.txt'
ok  21 [      7/      1] <  53> 'write_to /mnt/glusterfs/0/test1.txt test-message1'
ok  22 [      7/      2] <  54> 'test-message1 cat /mnt/glusterfs/0/test1.txt'
ok  23 [      7/      2] <  55> 'test-message0 cat /mnt/glusterfs/1/test1.txt'
not ok  24 [   1014/      6] <  58> 'test-message0 cat /mnt/glusterfs/1/test1.txt' -> 'Got "test-message1" instead of "test-message0"'
ok  25 [  30018/      6] <  61> 'test-message1 cat /mnt/glusterfs/1/test1.txt'
ok  26 [     10/    111] <  63> 'gluster --mode=script --wignore volume set patchy performance.quick-read-cache-invalidation on'
ok  27 [     12/    113] <  64> 'gluster --mode=script --wignore volume set patchy performance.cache-invalidation on'
ok  28 [     13/      3] <  66> 'write_to /mnt/glusterfs/0/test2.txt test-message0'
ok  29 [      9/      5] <  67> 'test-message0 cat /mnt/glusterfs/0/test2.txt'
ok  30 [      9/      3] <  68> 'test-message0 cat /mnt/glusterfs/1/test2.txt'
ok  31 [      7/      2] <  70> 'write_to /mnt/glusterfs/0/test2.txt test-message1'
ok  32 [      7/      4] <  71> 'test-message1 cat /mnt/glusterfs/0/test2.txt'
ok  33 [      7/      3] <  72> 'test-message1 cat /mnt/glusterfs/1/test2.txt'
Failed 1/33 subtests 

(sometimes it passes!)

Originally posted by @mykaul in #3795 (comment)