Commits on Aug 24, 2023

1. ZIL: Second attempt to reduce scope of zl_issuer_lock. …

   The previous patch openzfs#14841 appeared to have significant flaw, causing
   deadlocks if zl_get_data callback got blocked waiting for TXG sync.  I
   already handled some of such cases in the original patch, but issue
    openzfs#14982 shown cases that were impossible to solve in that design.
   
   This patch fixes the problem by postponing log blocks allocation till
   the very end, just before the zios issue, leaving nothing blocking after
   that point to cause deadlocks.  Before that point though any sleeps are
   now allowed, not causing sync thread blockage.  This require slightly
   more complicated lwb state machine to allocate blocks and issue zios
   in proper order.  But with removal of special early issue workarounds
   the new code is much cleaner now, and should even be more efficient.
   
   Since this patch uses null zios between write, I've found that null
   zios do not wait for logical children ready status in zio_ready(),
   that makes parent write to proceed prematurely, producing incorrect
   log blocks.  Added ZIO_CHILD_LOGICAL_BIT to zio_wait_for_children()
   fixes it.
   
   Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
   Sponsored by:	iXsystems, Inc.

   

   amotin committed Aug 24, 2023
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