On Friday, February 17, 2012, Alan Stern wrote:
> 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 at rowland.harvard.edu>
> CC: Tejun Heo <tj at kernel.org>
> CC: <stable at kernel.org>
Acked-by: Rafael J. Wysocki <rjw at sisk.pl>
Thanks,
Rafael
> ---
>
> I'm not sure who to send this patch to, since it is relevant to both
> the block and PM subsystems. Jens, is it okay if Rafael takes it?
>
>
>
> block/genhd.c | 10 +++++-----
> include/linux/workqueue.h | 4 ++++
> kernel/workqueue.c | 7 ++++++-
> 3 files changed, 15 insertions(+), 6 deletions(-)
>
> Index: usb-3.3/block/genhd.c
> ===================================================================
> --- usb-3.3.orig/block/genhd.c
> +++ usb-3.3/block/genhd.c
> @@ -1475,9 +1475,9 @@ static void __disk_unblock_events(struct
> intv = disk_events_poll_jiffies(disk);
> set_timer_slack(&ev->dwork.timer, intv / 4);
> if (check_now)
> - queue_delayed_work(system_nrt_wq, &ev->dwork, 0);
> + queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, 0);
> else if (intv)
> - queue_delayed_work(system_nrt_wq, &ev->dwork, intv);
> + queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, intv);
> out_unlock:
> spin_unlock_irqrestore(&ev->lock, flags);
> }
> @@ -1521,7 +1521,7 @@ void disk_flush_events(struct gendisk *d
> ev->clearing |= mask;
> if (!ev->block) {
> cancel_delayed_work(&ev->dwork);
> - queue_delayed_work(system_nrt_wq, &ev->dwork, 0);
> + queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, 0);
> }
> spin_unlock_irq(&ev->lock);
> }
> @@ -1558,7 +1558,7 @@ unsigned int disk_clear_events(struct ge
>
> /* uncondtionally schedule event check and wait for it to finish */
> disk_block_events(disk);
> - queue_delayed_work(system_nrt_wq, &ev->dwork, 0);
> + queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, 0);
> flush_delayed_work(&ev->dwork);
> __disk_unblock_events(disk, false);
>
> @@ -1595,7 +1595,7 @@ static void disk_events_workfn(struct wo
>
> intv = disk_events_poll_jiffies(disk);
> if (!ev->block && intv)
> - queue_delayed_work(system_nrt_wq, &ev->dwork, intv);
> + queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, intv);
>
> spin_unlock_irq(&ev->lock);
>
> Index: usb-3.3/include/linux/workqueue.h
> ===================================================================
> --- usb-3.3.orig/include/linux/workqueue.h
> +++ usb-3.3/include/linux/workqueue.h
> @@ -289,12 +289,16 @@ enum {
> *
> * system_freezable_wq is equivalent to system_wq except that it's
> * freezable.
> + *
> + * system_nrt_freezable_wq is equivalent to system_nrt_wq except that
> + * it's freezable.
> */
> extern struct workqueue_struct *system_wq;
> extern struct workqueue_struct *system_long_wq;
> extern struct workqueue_struct *system_nrt_wq;
> extern struct workqueue_struct *system_unbound_wq;
> extern struct workqueue_struct *system_freezable_wq;
> +extern struct workqueue_struct *system_nrt_freezable_wq;
>
> extern struct workqueue_struct *
> __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
> Index: usb-3.3/kernel/workqueue.c
> ===================================================================
> --- usb-3.3.orig/kernel/workqueue.c
> +++ usb-3.3/kernel/workqueue.c
> @@ -253,11 +253,13 @@ struct workqueue_struct *system_long_wq
> 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>
> @@ -3833,8 +3835,11 @@ 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);
>
>
>
