dc732906c2
This patch introduces a new HIF_MAY_DEMOTE flag and infrastructure that will allow glocks to be demoted automatically on locking conflicts. When a locking request comes in that isn't compatible with the locking state of an active holder and that holder has the HIF_MAY_DEMOTE flag set, the holder will be demoted before the incoming locking request is granted. Note that this mechanism demotes active holders (with the HIF_HOLDER flag set), while before we were only demoting glocks without any active holders. This allows processes to keep hold of locks that may form a cyclic locking dependency; the core glock logic will then break those dependencies in case a conflicting locking request occurs. We'll use this to avoid giving up the inode glock proactively before faulting in pages. Processes that allow a glock holder to be taken away indicate this by calling gfs2_holder_allow_demote(), which sets the HIF_MAY_DEMOTE flag. Later, they call gfs2_holder_disallow_demote() to clear the flag again, and then they check if their holder is still queued: if it is, they are still holding the glock; if it isn't, they can re-acquire the glock (or abort). Signed-off-by: Bob Peterson <rpeterso@redhat.com> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Linux kernel
============
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