diff options
author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2014-08-25 20:25:06 -0700 |
---|---|---|
committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2014-09-18 16:22:27 -0700 |
commit | dd56af42bd829c6e770ed69812bd65a04eaeb1e4 (patch) | |
tree | 6d510ac693c3dfb05dcc383cb60acd3e1e8cab6c /Documentation/locking | |
parent | ec4518aad8329364af373f4bf7f4eff25a01a339 (diff) | |
download | op-kernel-dev-dd56af42bd829c6e770ed69812bd65a04eaeb1e4.zip op-kernel-dev-dd56af42bd829c6e770ed69812bd65a04eaeb1e4.tar.gz |
rcu: Eliminate deadlock between CPU hotplug and expedited grace periods
Currently, the expedited grace-period primitives do get_online_cpus().
This greatly simplifies their implementation, but means that calls
to them holding locks that are acquired by CPU-hotplug notifiers (to
say nothing of calls to these primitives from CPU-hotplug notifiers)
can deadlock. But this is starting to become inconvenient, as can be
seen here: https://lkml.org/lkml/2014/8/5/754. The problem in this
case is that some developers need to acquire a mutex from a CPU-hotplug
notifier, but also need to hold it across a synchronize_rcu_expedited().
As noted above, this currently results in deadlock.
This commit avoids the deadlock and retains the simplicity by creating
a try_get_online_cpus(), which returns false if the get_online_cpus()
reference count could not immediately be incremented. If a call to
try_get_online_cpus() returns true, the expedited primitives operate as
before. If a call returns false, the expedited primitives fall back to
normal grace-period operations. This falling back of course results in
increased grace-period latency, but only during times when CPU hotplug
operations are actually in flight. The effect should therefore be
negligible during normal operation.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Tested-by: Lan Tianyu <tianyu.lan@intel.com>
Diffstat (limited to 'Documentation/locking')
0 files changed, 0 insertions, 0 deletions