Block: use a freezable workqueue for disk-event polling

BugLink: http://bugs.launchpad.net/bugs/959470

commit 62d3c5439c534b0e6c653fc63e6d8c67be3a57b1 upstream.

This patch (as1519) fixes a bug in the block layer's disk-events
polling.  The polling is done by a work routine queued on the
system_nrt_wq workqueue.  Since that workqueue isn't freezable, the
polling continues even in the middle of a system sleep transition.

Obviously, polling a suspended drive for media changes and such isn't
a good thing to do; in the case of USB mass-storage devices it can
lead to real problems requiring device resets and even re-enumeration.

The patch fixes things by creating a new system-wide, non-reentrant,
freezable workqueue and using it for disk-events polling.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index aec02b6a1c4..1456daba9a0 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -252,11 +252,13 @@ struct workqueue_struct *system_long_wq __read_mostly;
 struct workqueue_struct *system_nrt_wq __read_mostly;
 struct workqueue_struct *system_unbound_wq __read_mostly;
 struct workqueue_struct *system_freezable_wq __read_mostly;
+struct workqueue_struct *system_nrt_freezable_wq __read_mostly;
 EXPORT_SYMBOL_GPL(system_wq);
 EXPORT_SYMBOL_GPL(system_long_wq);
 EXPORT_SYMBOL_GPL(system_nrt_wq);
 EXPORT_SYMBOL_GPL(system_unbound_wq);
 EXPORT_SYMBOL_GPL(system_freezable_wq);
+EXPORT_SYMBOL_GPL(system_nrt_freezable_wq);
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/workqueue.h>
@@ -3796,8 +3798,11 @@ static int __init init_workqueues(void)
                                             WQ_UNBOUND_MAX_ACTIVE);
         system_freezable_wq = alloc_workqueue("events_freezable",
                                               WQ_FREEZABLE, 0);
+        system_nrt_freezable_wq = alloc_workqueue("events_nrt_freezable",
+                        WQ_NON_REENTRANT | WQ_FREEZABLE, 0);
         BUG_ON(!system_wq || !system_long_wq || !system_nrt_wq ||
-               !system_unbound_wq || !system_freezable_wq);
+               !system_unbound_wq || !system_freezable_wq ||
+                !system_nrt_freezable_wq);
         return 0;
 }
 early_initcall(init_workqueues);