linux-sg2042/kernel/rcu
Paul E. McKenney dd56af42bd 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>
2014-09-18 16:22:27 -07:00
..
Makefile rcutorture: Abstract rcu_torture_random() 2014-02-23 09:00:58 -08:00
rcu.h rcu: Fix __rcu_reclaim() to use true/false for bool 2014-07-09 09:15:32 -07:00
rcutorture.c rcutorture: Rename rcutorture_runnable parameter 2014-09-16 13:41:44 -07:00
srcu.c rcu: Eliminate read-modify-write ACCESS_ONCE() calls 2014-07-09 09:14:49 -07:00
tiny.c Merge branch 'rcu-tasks.2014.09.10a' into HEAD 2014-09-16 10:10:44 -07:00
tiny_plugin.h rcu: Protect uses of ->jiffies_stall with ACCESS_ONCE() 2014-04-29 08:44:41 -07:00
tree.c rcu: Eliminate deadlock between CPU hotplug and expedited grace periods 2014-09-18 16:22:27 -07:00
tree.h Merge branch 'rcu-tasks.2014.09.10a' into HEAD 2014-09-16 10:10:44 -07:00
tree_plugin.h rcu: Eliminate deadlock between CPU hotplug and expedited grace periods 2014-09-18 16:22:27 -07:00
tree_trace.c rcu: Stop tracking FSF's postal address 2014-02-17 15:01:37 -08:00
update.c Merge branch 'rcu-tasks.2014.09.10a' into HEAD 2014-09-16 10:10:44 -07:00