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SubjectRe: [PATCH] fix NULL-pointer dereference on scsi_run_queue
On 08/04/12 22:36, Mike Christie wrote:
> On 08/04/2012 03:18 PM, Bart Van Assche wrote:
>> On 08/04/12 16:46, Mike Christie wrote:
>>> I think we have to have scsi-ml do a get_device when a sdev is added to
>>> the starved entry and then do a put_device when it is removed (must do
>>> these under the host lock for the starved entry case too). I am not sure
>>> if that is just a hack/papering-over of the problem and there are more
>>> issues like this.
>>
>> That would result in a more complex patch than the patch at the start of
>> this thread, isn't it ?
>
> Yaah, but the original patch in this thread is still racey isn't it?

Indeed. How about the patch below ? Scsi devices are removed from
starved_list after blk_cleanup_queue() and before put_device(). That
guarantees that inside scsi_run_queue() get_device() under host lock
will succeed.

---
drivers/scsi/scsi_lib.c | 5 +++++
drivers/scsi/scsi_sysfs.c | 7 ++++++-
2 files changed, 11 insertions(+), 1 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index ffd7773..bd7daec 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -452,10 +452,15 @@ static void scsi_run_queue(struct request_queue *q)
continue;
}

+ get_device(&sdev->sdev_gendev);
spin_unlock(shost->host_lock);
+
spin_lock(sdev->request_queue->queue_lock);
__blk_run_queue(sdev->request_queue);
spin_unlock(sdev->request_queue->queue_lock);
+
+ put_device(&sdev->sdev_gendev);
+
spin_lock(shost->host_lock);
}
/* put any unprocessed entries back */
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 093d4f6..44f232e 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -348,7 +348,6 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
starget->reap_ref++;
list_del(&sdev->siblings);
list_del(&sdev->same_target_siblings);
- list_del(&sdev->starved_entry);
spin_unlock_irqrestore(sdev->host->host_lock, flags);

cancel_work_sync(&sdev->event_work);
@@ -956,6 +955,8 @@ int scsi_sysfs_add_sdev(struct scsi_device *sdev)
void __scsi_remove_device(struct scsi_device *sdev)
{
struct device *dev = &sdev->sdev_gendev;
+ struct Scsi_Host *shost = sdev->host;
+ unsigned long flags;

if (sdev->is_visible) {
if (scsi_device_set_state(sdev, SDEV_CANCEL) != 0)
@@ -977,6 +978,10 @@ void __scsi_remove_device(struct scsi_device *sdev)
blk_cleanup_queue(sdev->request_queue);
cancel_work_sync(&sdev->requeue_work);

+ spin_lock_irqsave(shost->host_lock, flags);
+ list_del(&sdev->starved_entry);
+ spin_unlock_irqrestore(shost->host_lock, flags);
+
if (sdev->host->hostt->slave_destroy)
sdev->host->hostt->slave_destroy(sdev);
transport_destroy_device(dev);
--
1.7.7



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