• Dave Chinner's avatar
    xfs: inform the xfsaild of the push target before sleeping · 9d7fef74
    Dave Chinner authored
    When trying to reserve log space, we find the amount of space
    we need, then go to sleep waiting for space. When we are
    woken, we try to push the tail of the log forward to make
    sure we have space available.
    
    Unfortunately, this means that if there is not space available, and
    everyone who needs space goes to sleep there is no-one left to push
    the tail of the log to make space available. Once we have a thread
    waiting for space to become available, the others queue up behind
    it in a FIFO, and none of them push the tail of the log.
    
    This can result in everyone going to sleep in xlog_grant_log_space()
    if the first sleeper races with the last I/O that moves the tail
    of the log forward. With no further I/O tomove the tail of the log,
    there is nothing to wake the sleepers and hence all transactions
    just stop.
    
    Fix this by making sure the xfsaild will create enough space for the
    transaction that is about to sleep by moving the push target far
    enough forwards to ensure that that the curent proceeees will have
    enough space available when it is woken. That is, we push the
    AIL before we go to sleep.
    
    Because we've inserted the log ticket into the queue before we've
    pushed and gone to sleep, subsequent transactions will wait behind
    this one. Hence we are guaranteed to have space available when we
    are woken.
    Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    9d7fef74
xfs_log.c 106 KB