7378 exported_lock held during nfs4 compound processing

Review Request #813 — Created Jan. 12, 2018 and updated — Latest diff uploaded

marcel
illumos-gate
master
7378
5b4e200...
general
Traditionally, rfs4_compound() holds a read lock on exported_lock during the
processing of the compound request. The processing of some OPs might take
several seconds. In our case, writes to a zfs filesystem can take very long if
the filesystem is at quota. In this case, zfs waits for the next txg to free
some space. This becomes problematic should someone need a write lock, like
share(). If there is a pending writer, it has to wait for all existing readers
to complete. During this time, all new readers also have to wait, effectively
rendering nfs4 service unresponsive.

The aim is to only acquire the exported_lock during nfs4 processing when
needed.


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