[Cluster-devel] [PATCH v6 10/19] gfs2: Introduce flag for glock holder auto-demotion

Andreas Grünbacher andreas.gruenbacher at gmail.com
Fri Aug 20 14:43:34 UTC 2021

Am Fr., 20. Aug. 2021 um 15:49 Uhr schrieb Steven Whitehouse
<swhiteho at redhat.com>:
> We always used to manage to avoid holding fs locks when copying to/from userspace
> to avoid these complications.

I realize the intent, but that goal has never actually been achieved.
Direct I/O has *always* been calling get_user_pages() while holding
the inode glock in deferred mode.

The situation is slightly different for buffered I/O, but we have the
same problem there at least since switching to iomap. (And it's a
fundamental property of iomap that we want to hold the inode glock
across multi-page mappings, not an implementation deficit.)

Here's a slightly outdated version of a test case that makes all
versions of gfs2 prior to this patch queue unhappy:


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