[Bugs] [Bug 1215592] Crash in dht_getxattr_cbk

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1215592



--- Comment #2 from Anand Avati <aavati at redhat.com> ---
COMMIT: http://review.gluster.org/10389 committed in master by Shyamsundar
Ranganathan (srangana at redhat.com) 
------
commit 6bde16f7dc4a43d85e488f25ad679abfd24e72d1
Author: Susant Palai <spalai at redhat.com>
Date:   Sun Apr 26 23:49:56 2015 +0530

    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 at redhat.com>
    Reviewed-on: http://review.gluster.org/10389
    Reviewed-by: Anuradha Talur <atalur at redhat.com>
    Reviewed-by: N Balachandran <nbalacha at redhat.com>
    Reviewed-by: Kotresh HR <khiremat at redhat.com>
    Tested-by: NetBSD Build System
    Tested-by: Gluster Build System <jenkins at build.gluster.com>
    Reviewed-by: Shyamsundar Ranganathan <srangana at redhat.com>

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