[PATCH v4 1/9] IB/srp: Fix a sporadic crash triggered by cable pulling

[Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>]

Avoid that the loops that iterate over the request ring can
encounter a pointer to a SCSI command in req->scmnd that is
no longer associated with that request. If the function
srp_unmap_data() is invoked twice for a SCSI command that is
not in flight then that would cause ib_fmr_pool_unmap() to
be invoked with an invalid pointer as argument, resulting in
a kernel oops.

Reported-by: Sagi Grimberg <sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Reference: http://thread.gmane.org/gmane.linux.drivers.rdma/19068/focus=19069
Signed-off-by: Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>
Reviewed-by: Sagi Grimberg <sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Cc: Roland Dreier <roland-BHEL68pLQRGGvPXPguhicg@public.gmane.org>
Cc: David Dillow <dave-i1Mk8JYDVaaSihdK6806/g@public.gmane.org>
Cc: Vu Pham <vu-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Cc: Sebastian Parschauer <sebastian.riemer-EIkl63zCoXaH+58JC4qpiA@public.gmane.org>
Cc: stable <stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
---
 drivers/infiniband/ulp/srp/ib_srp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index 66a908b..5b2bed8 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -1594,6 +1594,12 @@ err_unmap:
 err_iu:
 	srp_put_tx_iu(target, iu, SRP_IU_CMD);
 
+	/*
+	 * Avoid that the loops that iterate over the request ring can
+	 * encounter a dangling SCSI command pointer.
+	 */
+	req->scmnd = NULL;
+
 	spin_lock_irqsave(&target->lock, flags);
 	list_add(&req->list, &target->free_reqs);
 
-- 
1.8.4.5

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