dht: tackle thread race in dht_getxattr_cbk

problem:
 1. When two threads execute in parallel in dht_getxattr_cbk
it may so happen that, both may find local->xattr to be NULL. As
a result dht_aggregate_xattr may not get executed.

 2. In dht_getxattr_cbk,

             thread1                         thread2
T1      this_call_cnt = 2 -1
T2                                this_call_cnt = 1 - 1
T3                                fills local_xattr
T4                                DHT_STACK_UNWIND -> local_wipe
T5      tries to dereference local
        which is already freed,
        leading to crash.

Solution:
 for problem1: Execute critical section inside frame lock
to resolve race.

 for problem2: Calculate this_call_count just before out section.

Change-Id: I9827ac8fafebb0c733a4e4f3c710b752f1cd45fa
BUG: 1215592
Signed-off-by: Susant Palai <spalai@redhat.com>
Reviewed-on: http://review.gluster.org/10389
Reviewed-by: Anuradha Talur <atalur@redhat.com>
Reviewed-by: N Balachandran <nbalacha@redhat.com>
Reviewed-by: Kotresh HR <khiremat@redhat.com>
Tested-by: NetBSD Build System
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>

0 files changed, 0 insertions, 0 deletions