IMPALA-1046: Fix race in io mgr with cancelled readers and OOM.
IMPALA-1046: Fix race in io mgr with cancelled readers and OOM.

Change-Id: I3bce1a0444bd40528a474fb53c3af4d2b53b4aa7
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3022
Reviewed-by: Srinath Shankar <3801481aac49ac3df829825a1d4dd7c1f9a518ae@cloudera.com>
Tested-by: jenkins
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3050
Reviewed-by: Nong Li <99a5e5f8f5911755b88e0b536d46aafa102bed41@cloudera.com>

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