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SubjectAS spin lock bugs
Hi,

Was looking at io tracking for cfq, and I think I found some spin lock
bugs in current as (current BK). as_update_iohist() runs from
add_request which is typically in process context. It could be run with
interrupts disabled though, either driver private stuff or using the
generic block layer tagging.

Anyways, as_update_iohist() grabs aic->lock without disabling
interrupts, while as_completed_request() typically runs at interrupt
time and grabs the same lock. Deadlock.

To be safe, both need to use the flags saving lock variants.

===== drivers/block/as-iosched.c 1.28 vs edited =====
--- 1.28/drivers/block/as-iosched.c Mon Nov 10 06:12:07 2003
+++ edited/drivers/block/as-iosched.c Thu Nov 13 11:37:47 2003
@@ -783,14 +783,14 @@
{
struct as_rq *arq = RQ_DATA(rq);
int data_dir = arq->is_sync;
- unsigned long thinktime;
+ unsigned long thinktime, flags;
sector_t seek_dist;

if (aic == NULL)
return;

if (data_dir == REQ_SYNC) {
- spin_lock(&aic->lock);
+ spin_lock_irqsave(&aic->lock, flags);

if (test_bit(AS_TASK_IORUNNING, &aic->state)
&& !atomic_read(&aic->nr_queued)
@@ -844,7 +844,7 @@
aic->seek_total = (aic->seek_total>>1)
+ (aic->seek_total>>2);

- spin_unlock(&aic->lock);
+ spin_unlock_irqrestore(&aic->lock, flags);
}
}

@@ -909,6 +909,7 @@
struct as_data *ad = q->elevator.elevator_data;
struct as_rq *arq = RQ_DATA(rq);
struct as_io_context *aic;
+ unsigned long flags;

WARN_ON(!list_empty(&rq->queuelist));

@@ -959,12 +960,12 @@
if (!aic)
return;

- spin_lock(&aic->lock);
+ spin_lock_irqsave(&aic->lock, flags);
if (arq->is_sync == REQ_SYNC) {
set_bit(AS_TASK_IORUNNING, &aic->state);
aic->last_end_request = jiffies;
}
- spin_unlock(&aic->lock);
+ spin_unlock_irqrestore(&aic->lock, flags);

put_io_context(arq->io_context);
}
--
Jens Axboe

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