Commits on Dec 20, 2022

1. deadlock between spa_errlog_lock and dp_config_rwlock …

   There is a lock order inversion deadlock between `spa_errlog_lock` and
   `dp_config_rwlock`:
   
   A thread in `spa_delete_dataset_errlog()` is running from a sync task.
   It is holding the `dp_config_rwlock` for writer (see
   `dsl_sync_task_sync()`), and waiting for the `spa_errlog_lock`.
   
   A thread in `dsl_pool_config_enter()` is holding the `spa_errlog_lock`
   (see `spa_get_errlog_size()`) and waiting for the `dp_config_rwlock` (as
   reader).
   
   Note that this was introduced by openzfs#12812.
   
   This commit address this by defining the lock ordering to be
   dp_config_rwlock first, then spa_errlog_lock / spa_errlist_lock.
   spa_get_errlog() and spa_get_errlog_size() can acquire the locks in this
   order, and then process_error_block() and get_head_and_birth_txg() can
   verify that the dp_config_rwlock is already held.
   
   Additionally, a buffer overrun in `spa_get_errlog()` is corrected.  Many
   code paths didn't check if `*count` got to zero, instead continuing to
   overwrite past the beginning of the userspace buffer at `uaddr`.
   
   Tested by having some errors in the pool (via `zinject -t data
   /path/to/file`), one thread running `zpool iostat 0.001`, and another
   thread runs `zfs destroy` (in a loop, although it hits the first time).
   This reproduces the problem easily without the fix, and works with the
   fix.
   
   Closes openzfs#14239
   Signed-off-by: Matthew Ahrens <mahrens@delphix.com>

   

   ahrens committed Dec 20, 2022
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