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pserialize(9) vs. TAILQ
I thought I kind of understood how pserialize(9) works, but the manual
* Perform the updates (e.g. remove data items from a list).
* At this point it is safe to destroy old data items.
My understanding is that, writers can update data structures between
mutex_enter() and pserialize_perform(), but that operation must be
done atomically, because at that point readers are still reading the
In pserialize_perform(), context switches are made on all CPUs. After
pserialize_perform(), all readers on all CPUs see the update data.
The data old data item is safely destroyed.
In the TAILQ case, where readers iterate a list by TAILQ_FOREACH(),
TAILQ_REMOVE() is safely used as the update operation, because:
- Readers only see tqe_next in TAILQ_FOREACH(), and
- Pointer assignment (done in TAILQ_REMOVE()) is atomic.
If this is correct, pserialize(9) should be updated to be clearer;
probably this TAILQ example is worth being added there.
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