Commits on Apr 4, 2024

1. Fix read errors race after block cloning …

   Investigating read errors triggering panic fixed in openzfs#16042 I've
   found that we have a race in a sync process between the moment
   dirty record for cloned block is removed and the moment dbuf is
   destroyed.  If dmu_buf_hold_array_by_dnode() take a hold on a
   cloned dbuf before it is synced/destroyed, then dbuf_read_impl()
   may see it still in DB_NOFILL state, but without the dirty record.
   Such case is not an error, but equivalent to DB_UNCACHED, since
   the dbuf block pointer is already updated by dbuf_write_ready().
   Unfortunately it is impossible to safely change the dbuf state
   to DB_UNCACHED there, since there may already be another cloning
   in progress, that dropped dbuf lock before creating a new dirty
   record, protected only by the range lock.
   
   Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
   Sponsored by:	iXsystems, Inc.

   

   amotin committed Apr 4, 2024
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