[Bugs] [Bug 1152902] Rebalance on a dispersed volume produces multiple errors in logs

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1152902



--- Comment #5 from Anand Avati <aavati at redhat.com> ---
COMMIT: http://review.gluster.org/8947 committed in master by Vijay Bellur
(vbellur at redhat.com) 
------
commit 306e6bf33fbaf5656764d01ad87452e265e2a6e9
Author: Xavier Hernandez <xhernandez at datalab.es>
Date:   Wed Oct 15 09:44:55 2014 +0200

    ec: Fix rebalance issues

    Some issues in ec xlator made that rebalance didn't complete
    successfully and generated some warnings and errors in the
    log. The most critical error was a race condition that caused
    false corruption detection when two specific operations were
    executed sequentially and they shared the same lock.

    This explains the problem:

    1. A setxattr is issued.
    2. setxattr: ec locks the inode before updating the xattr.
    3. setxattr: The xattr is updated.
    4. setxattr: Upper xlator is notified that the operation completed.
    5. setxattr: A background task is initiated to update the version
                 of the file.
    6. A stat is issued on the same file.
    7. stat: Since the lock is already acquired, it's reused.
    8. stat: A lookup is issued to determine version and size
             information of the file.

    At this point, operations 5 and 8 can interfere. This can make that
    lookup sees different information on each brick, determining that
    some bricks are corrupted and incorrectly excluding them from the
    operation and initiating a self-heal. In some cases this false
    detection combined with self-heal could lead to invalid updates of
    the trusted.ec.size xattr, leaving the file smaller than it should
    be.

    This only happens if the first operation does not perform a lookup,
    because chained operations reuse the information returned by the
    previous one, avoiding this kind of problems.

    To solve this, now the background update is executed atomically with
    the posterior unlock. This avoids some reuses of the lock while
    updating. However this reduces performance because the window in
    which new requests can reuse the lock is much smaller now. This has
    been alleviated by using the same technique implemented in AFR (i.e.
    waiting some time before releasing the lock).

    Some minor changes also introduced in this patch:

    * Bug in management of 'trusted.glusterfs.pathinfo' that was writing
      beyond the allocated space.
    * Uninitialized variable.
    * trusted.ec.config was not created for regular files created with
      mknod.
    * An invalid state was used in access fop.

    Change-Id: Idfaf69578ed04dbac97a62710326729715b9b395
    BUG: 1152902
    Signed-off-by: Xavier Hernandez <xhernandez at datalab.es>
    Reviewed-on: http://review.gluster.org/8947
    Tested-by: Gluster Build System <jenkins at build.gluster.com>
    Reviewed-by: Vijay Bellur <vbellur at redhat.com>

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