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Subject[18/20] SCSI: scsi_dh: check queuedata pointer before proceeding further
2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: "Moger, Babu" <Babu.Moger@netapp.com>

commit a18a920c70d48a8e4a2b750d8a183b3c1a4be514 upstream.

This patch validates sdev pointer in scsi_dh_activate before proceeding further.

Without this check we might see the panic as below. I have seen this
panic multiple times..

Call trace:

#0 [ffff88007d647b50] machine_kexec at ffffffff81020902
#1 [ffff88007d647ba0] crash_kexec at ffffffff810875b0
#2 [ffff88007d647c70] oops_end at ffffffff8139c650
#3 [ffff88007d647c90] __bad_area_nosemaphore at ffffffff8102dd15
#4 [ffff88007d647d50] page_fault at ffffffff8139b8cf
[exception RIP: scsi_dh_activate+0x82]
RIP: ffffffffa0041922 RSP: ffff88007d647e00 RFLAGS: 00010046
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00000000000093c5
RDX: 00000000000093c5 RSI: ffffffffa02e6640 RDI: ffff88007cc88988
RBP: 000000000000000f R8: ffff88007d646000 R9: 0000000000000000
R10: ffff880082293790 R11: 00000000ffffffff R12: ffff88007cc88988
R13: 0000000000000000 R14: 0000000000000286 R15: ffff880037b845e0
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0000
#5 [ffff88007d647e38] run_workqueue at ffffffff81060268
#6 [ffff88007d647e78] worker_thread at ffffffff81060386
#7 [ffff88007d647ee8] kthread at ffffffff81064436
#8 [ffff88007d647f48] kernel_thread at ffffffff81003fba
Signed-off-by: Babu Moger <babu.moger@netapp.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/scsi/device_handler/scsi_dh.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/drivers/scsi/device_handler/scsi_dh.c
+++ b/drivers/scsi/device_handler/scsi_dh.c
@@ -432,7 +432,12 @@ int scsi_dh_activate(struct request_queu

spin_lock_irqsave(q->queue_lock, flags);
sdev = q->queuedata;
- if (sdev && sdev->scsi_dh_data)
+ if (!sdev) {
+ spin_unlock_irqrestore(q->queue_lock, flags);
+ return SCSI_DH_NOSYS;
+ }
+
+ if (sdev->scsi_dh_data)
scsi_dh = sdev->scsi_dh_data->scsi_dh;
if (!scsi_dh || !get_device(&sdev->sdev_gendev))
err = SCSI_DH_NOSYS;



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