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Subject[set5 PATCH 6/6] scsi: fix hot unplug vs async scan race
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Date
The following crash results from cases where the end_device has been
removed before scsi_sysfs_add_sdev has had a chance to run.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000098
IP: [<ffffffff8115e100>] sysfs_create_dir+0x32/0xb6
...
Call Trace:
[<ffffffff8125e4a8>] kobject_add_internal+0x120/0x1e3
[<ffffffff81075149>] ? trace_hardirqs_on+0xd/0xf
[<ffffffff8125e641>] kobject_add_varg+0x41/0x50
[<ffffffff8125e70b>] kobject_add+0x64/0x66
[<ffffffff8131122b>] device_add+0x12d/0x63a
[<ffffffff814b65ea>] ? _raw_spin_unlock_irqrestore+0x47/0x56
[<ffffffff8107de15>] ? module_refcount+0x89/0xa0
[<ffffffff8132f348>] scsi_sysfs_add_sdev+0x4e/0x28a
[<ffffffff8132dcbb>] do_scan_async+0x9c/0x145
...teach scsi_sysfs_add_devices() to check for deleted devices() before
trying to add them, and teach scsi_remove_target() how to remove targets
that have not been added via device_add().

Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Robert Love <robert.w.love@intel.com>
Cc: Nagalakshmi Nandigama <Nagalakshmi.Nandigama@lsi.com>
Cc: Kashyap Desai <kashyap.desai@lsi.com>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: <stable@vger.kernel.org>
Reported-by: Dariusz Majchrzak <dariusz.majchrzak@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/scsi/scsi_scan.c | 3 +++
drivers/scsi/scsi_sysfs.c | 41 ++++++++++++++++++++++++++---------------
2 files changed, 29 insertions(+), 15 deletions(-)
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 03ebb37..56a9379 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -1702,6 +1702,9 @@ static void scsi_sysfs_add_devices(struct Scsi_Host *shost)
{
struct scsi_device *sdev;
shost_for_each_device(sdev, shost) {
+ /* target removed before the device could be added */
+ if (sdev->sdev_state == SDEV_DEL)
+ continue;
if (!scsi_host_scan_allowed(shost) ||
scsi_sysfs_add_sdev(sdev) != 0)
__scsi_remove_device(sdev);
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 04c2a27..f888aad 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -1000,7 +1000,6 @@ static void __scsi_remove_target(struct scsi_target *starget)
struct scsi_device *sdev;

spin_lock_irqsave(shost->host_lock, flags);
- starget->reap_ref++;
restart:
list_for_each_entry(sdev, &shost->__devices, siblings) {
if (sdev->channel != starget->channel ||
@@ -1014,14 +1013,6 @@ static void __scsi_remove_target(struct scsi_target *starget)
goto restart;
}
spin_unlock_irqrestore(shost->host_lock, flags);
- scsi_target_reap(starget);
-}
-
-static int __remove_child (struct device * dev, void * data)
-{
- if (scsi_is_target_device(dev))
- __scsi_remove_target(to_scsi_target(dev));
- return 0;
}

/**
@@ -1034,14 +1025,34 @@ static int __remove_child (struct device * dev, void * data)
*/
void scsi_remove_target(struct device *dev)
{
- if (scsi_is_target_device(dev)) {
- __scsi_remove_target(to_scsi_target(dev));
- return;
+ struct Scsi_Host *shost = dev_to_shost(dev->parent);
+ struct scsi_target *starget, *found;
+ unsigned long flags;
+
+ restart:
+ found = NULL;
+ spin_lock_irqsave(shost->host_lock, flags);
+ list_for_each_entry(starget, &shost->__targets, siblings) {
+ if (starget->state == STARGET_DEL)
+ continue;
+ if (starget->dev.parent == dev || &starget->dev == dev) {
+ found = starget;
+ found->reap_ref++;
+ break;
+ }
}
+ spin_unlock_irqrestore(shost->host_lock, flags);

- get_device(dev);
- device_for_each_child(dev, NULL, __remove_child);
- put_device(dev);
+ if (found) {
+ __scsi_remove_target(found);
+ scsi_target_reap(found);
+ /* in the case where @dev has multiple starget children,
+ * continue removing.
+ *
+ * FIXME: does such a case exist?
+ */
+ goto restart;
+ }
}
EXPORT_SYMBOL(scsi_remove_target);



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