[Bugs] [Bug 1412909] [Arbiter] IO's Halted and heal info command hung

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1412909

Pranith Kumar K <pkarampu at redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|bugs at gluster.org            |pkarampu at redhat.com



--- Comment #1 from Pranith Kumar K <pkarampu at redhat.com> ---
When we have cascading locks with same lk-owner there is a possibility for
    a deadlock to happen. One example is as follows:

    self-heal takes a lock in data-domain for big name with 256 chars of
"aaaa...a"
    and starts heal in a 3-way replication when brick-0 is offline and healing
from
    brick-1 to brick-2 is in progress. So this lock is active on brick-1 and
    brick-2. Now brick-0 comes online and an operation wants to take full lock
and
    the lock is granted at brick-0 and it is waiting for lock on brick-1. As
part
    of entry healing it takes full locks on all the available bricks and then
    proceeds with healing the entry. Now this lock will start waiting on
brick-0
    because some other operation already has a granted lock on it. This leads
to a
    deadlock. Operation is waiting for unlock on "aaaa..." by heal where as
heal is
    waiting for the operation to unlock on brick-0. Initially I thought this is
    happening because healing is trying to take a lock on all the available
bricks
    instead of just the bricks that are participating in heal. But later
realized
    that same kind of deadlock can happen if a brick goes down after the heal
    starts but comes back before it completes. So the essential problem is the
    cascading locks with same lk-owner which were added for backward
compatibility
    with afr-v1 which can be safely removed now that versions with afr-v1 are
    already EOL. This patch removes the compatibility with v1 which requires
    cascading locks with same lk-owner.

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