[Bugs] [Bug 1392289] gfapi clients crash while using async calls due to double fd_unref

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1392289



--- Comment #3 from Worker Ant <bugzilla-bot at gluster.org> ---
COMMIT: http://review.gluster.org/15780 committed in release-3.7 by Raghavendra
Talur (rtalur at redhat.com) 
------
commit f593a4d7d1cd972e2fa65d1dac471d0bebee7235
Author: Raghavendra Talur <rtalur at redhat.com>
Date:   Wed Nov 2 19:51:26 2016 +0530

    gfapi: async fops should unref in callbacks

    If fd is unref'd at the end of async call then the unref in cbks would
    lead to double unref and possible crash. Removing duplicate unrefs.

    Added unref only in failure cases.

    This backport to 3.7 branch does not have tests because gfapi tests are
    not configured properly on 3.7 branch.

    Details:
    All glfd based calls in libgfapi, except for glfs_open and glfs_close,
    behave in the same way. At the start of the operation, they take a ref
    on glfd and fd. At the end of the operation, they unref it. Async calls
    are a little different as they unref in the cbk function. A successfull
    open call does not unref either the glfd or fd, thereby functioning as a
    reference for a OPEN file object. glfs_close makes a syncop_flush call
    sandwiched between a fd ref and unref(this can be removed, more on this
    below), followed by a call to glfs_mark_glfd_for_deletion which unrefs
    glfd and also calls glfs_fd_destroy as a release function thereby doing
    a unref on fd too.

    Functionally, there is no problem with how everything works when as
    described above. However, it is a little non-intuitive that we need to
    perform a fd_unref as a consequence of a implicit fd_ref that happens
    within glfs_resolve_fd. As we perform a GF_REF_GET(glfd) at the start of
    every operation, it would be worthwhile to remove the fd_ref that
    glfs_resovle_fd takes and do away with explicit fd_unref()s at the end
    of every operation. This is the same reason why we don't need the fd_ref
    in glfs_close. This is however not in the scope of this patch.

    Change-Id: I86b1d3b2ad846b16ea527d541dc82b5e90b0ba85
    BUG: 1392289
    Signed-off-by: Raghavendra Talur <rtalur at redhat.com>
    Reviewed-on: http://review.gluster.org/15768
    Smoke: Gluster Build System <jenkins at build.gluster.org>
    NetBSD-regression: NetBSD Build System <jenkins at build.gluster.org>
    Reviewed-by: Rajesh Joseph <rjoseph at redhat.com>
    Reviewed-by: Xavier Hernandez <xhernandez at datalab.es>
    Reviewed-by: soumya k <skoduri at redhat.com>
    Reviewed-by: Prasanna Kumar Kalever <pkalever at redhat.com>
    CentOS-regression: Gluster Build System <jenkins at build.gluster.org>
    Reviewed-by: Shyamsundar Ranganathan <srangana at redhat.com>
    (cherry picked from commit e65738818dd22462ec00dda021566654d1c702b1)
    Reviewed-on: http://review.gluster.org/15780

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