[Bugs] [Bug 1427012] Disconnects in nfs mount leads to IO hang and mount inaccessible

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1427012



--- Comment #4 from Worker Ant <bugzilla-bot at gluster.org> ---
COMMIT: https://review.gluster.org/16784 committed in master by Raghavendra G
(rgowdapp at redhat.com) 
------
commit 773f32caf190af4ee48818279b6e6d3c9f2ecc79
Author: Raghavendra G <rgowdapp at redhat.com>
Date:   Tue Feb 28 13:13:59 2017 +0530

    rpc/clnt: remove locks while notifying CONNECT/DISCONNECT

    Locking during notify was introduced as part of commit
    aa22f24f5db7659387704998ae01520708869873 [1]. The fix was introduced
    to fix out-of-order CONNECT/DISCONNECT events from rpc-clnt to parent
    xlators [2]. However as part of handling DISCONNECT protocol/client
    does unwind saved frames (with failure) waiting for responses. This
    saved_frames_unwind can be a costly operation and hence ideally
    shouldn't be included in the critical section of notifylock, as it
    unnecessarily delays the reconnection to same brick. Also, its not a
    good practise to pass control to other xlators holding a lock as it
    can lead to deadlocks. So, this patch removes locking in rpc-clnt
    while notifying parent xlators.

    To fix [2], two changes are present in this patch:

    * notify DISCONNECT before cleaning up rpc connection (same as commit
      a6b63e11b7758cf1bfcb6798, patch [3]).
    * protocol/client uses rpc_clnt_cleanup_and_start, which cleans up rpc
      connection and does a start while handling a DISCONNECT event from
      rpc. Note that patch [3] was reverted as rpc_clnt_start called in
      quick_reconnect path of protocol/client didn't invoke connect on
      transport as the connection was not cleaned up _yet_ (as cleanup was
      moved post notification in rpc-clnt). This resulted in clients never
      attempting connect to bricks.

    Note that one of the neater ways to fix [2] (without using locks) is
    to introduce generation numbers to map CONNECT and DISCONNECTS across
    epochs and ignore DISCONNECT events if they don't belong to current
    epoch. However, this approach is a bit complex to implement and
    requires time. So, current patch is a hacky stop-gap fix till we come
    up with a more cleaner solution.

    [1] http://review.gluster.org/15916
    [2] https://bugzilla.redhat.com/show_bug.cgi?id=1386626
    [3] http://review.gluster.org/15681

    Change-Id: I62daeee8bb1430004e28558f6eb133efd4ccf418
    Signed-off-by: Raghavendra G <rgowdapp at redhat.com>
    BUG: 1427012
    Reviewed-on: https://review.gluster.org/16784
    Smoke: Gluster Build System <jenkins at build.gluster.org>
    Reviewed-by: Milind Changire <mchangir at redhat.com>
    NetBSD-regression: NetBSD Build System <jenkins at build.gluster.org>
    CentOS-regression: Gluster Build System <jenkins at build.gluster.org>

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