Hi,
while working on LKCD I found out common block device issue.
LKCD uses generic_unplug_device() to finish disk IO in case of blockdev kernel core dump.
I found out that after calling of generic_unplug_device() IRQs become implicitly enabled (it is supposed that IRQs are disabled).
I looked at generic_unplug_device() code and found out that function lose state of irq flags, it use spin_lock_irq()/spin_unlock_irq() instead of spin_lock_irqsave()/spin_unlock_irqrestore():
void generic_unplug_device(request_queue_t *q)
{
spin_lock_irq(q->queue_lock);
__generic_unplug_device(q);
spin_unlock_irq(q->queue_lock);
}
generic_unplug_device() - is a method to unplug the block device, named unplug_fn in struct request_queue.
I've compared generic_unplug_device() with other methods:
file drivers/md/raid5.c ...
static void raid5_unplug_device(request_queue_t *q)
{
mddev_t *mddev = q->queuedata;
raid5_conf_t *conf = mddev_to_conf(mddev);
unsigned long flags;
spin_lock_irqsave(&conf->device_lock, flags);
if (blk_remove_plug(q)) {
conf->seq_flush++;
raid5_activate_delayed(conf);
}
md_wakeup_thread(mddev->thread);
spin_unlock_irqrestore(&conf->device_lock, flags);
unplug_slaves(mddev);
}
file drivers/block/umem.c ...
static void mm_unplug_device(request_queue_t *q)
{
struct cardinfo *card = q->queuedata;
unsigned long flags;
spin_lock_irqsave(&card->lock, flags);
if (blk_remove_plug(q))
activate(card);
spin_unlock_irqrestore(&card->lock, flags);
}
As you can see raid5_unplug_device() and mm_unplug_device() are using
spin_lock_irqsave()/spin_unlock_irqrestore(), instead of spin_lock_irq()/spin_unlock_irq().
I found out that generic_unplug_device() is used not only in LKCD, so I suggest to switch generic_unplug_device() to spin_lock_irqsave()/spin_unlock_irqrestore() to prevent implicitly losing of IRQ flags.
Here is patch against kernel 2.6.21.1.
Please CC me to answers/comments.
Thanks.
Signed-off-by: Konstantin Baydarov <[email protected]>
block/ll_rw_blk.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
Index: linux-2.6.21.1/block/ll_rw_blk.c
===================================================================
--- linux-2.6.21.1.orig/block/ll_rw_blk.c
+++ linux-2.6.21.1/block/ll_rw_blk.c
@@ -1602,9 +1602,11 @@ EXPORT_SYMBOL(__generic_unplug_device);
**/
void generic_unplug_device(request_queue_t *q)
{
- spin_lock_irq(q->queue_lock);
+ unsigned long flags;
+
+ spin_lock_irqsave(q->queue_lock, flags);
__generic_unplug_device(q);
- spin_unlock_irq(q->queue_lock);
+ spin_unlock_irqrestore(q->queue_lock, flags);
}
EXPORT_SYMBOL(generic_unplug_device);
-
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