Zach Brown c1d435937e scoutfs: remove dentry invalidation relaxing ...

We walk the list of dentries in subdirs on lock invalidation.  This can
be a large number so we were trying to back off and give other tasks a
chance to schedule and other processes a chance to grab the parent lock
while we were iterating.

The method for backing off saved our position in the list by getting a
reference on a child dentry.  It dropped that reference after resuming
iteration.

But it dropped the reference while holding the parent's lock.  This is a
deadlock if the put tries to finally remove the dentry because it's been
unhashed.  We saw this deadlock in practice, the crash dump showed us in
the final dentry_kill with the parent locked.

Let's just get rid of this premature optimization entirely.  Both memory
pressure and site logistics will tend to keep child lists in parents
reasonably small.  A CPU can burn through the locks and list entries for
quite a few entries before anything will notice.  We can revisit the hot
spot later it if bubbles to the surface.

Signed-off-by: Zach Brown <zab@versity.com>

2017-12-11 14:20:56 -06:00

kmod

scoutfs: remove dentry invalidation relaxing

2017-12-11 14:20:56 -06:00

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