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Subject[PATCH] ib-release-locks-in-the-proper-order
Please consider the following patch - originally from Steven Rostedt. 
It solves a problem for rt which is very sensitive to the lock ordering.
It should have a no impact on non-rt.

The patch applies to current tip/master - but it is fine with me if it
would be more appropriate for one of the infiniband people to take it.

Thanks

From e533f2b9ee9b0bd95aaa4c3369e79b350c9895d3 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <srostedt@redhat.com>
Date: Mon, 21 Sep 2009 21:23:46 +0200
Subject: [PATCH] ib: release locks in the proper order

RT is very sensitive to the order locks are taken and released
wrt read write locks. We must do

lock(a);
lock(b);
lock(c);

[...]

unlock(c);
unlock(b);
unlock(a);

otherwise bad things can happen.

Signed-off-by: Ken Cox <jkc@redhat.com>
Signed-off-by: Clark Williams <williams@redhat.com>
Signed-off-by: John Kacur <jkacur@redhat.com>
---
drivers/infiniband/core/uverbs_cmd.c | 20 ++++++++++----------
1 files changed, 10 insertions(+), 10 deletions(-)
diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
index 56feab6..5ea66e1 100644
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -1116,12 +1116,12 @@ ssize_t ib_uverbs_create_qp(struct ib_uverbs_file *file,
goto err_copy;
}

- put_pd_read(pd);
- put_cq_read(scq);
- if (rcq != scq)
- put_cq_read(rcq);
if (srq)
put_srq_read(srq);
+ if (rcq != scq)
+ put_cq_read(rcq);
+ put_cq_read(scq);
+ put_pd_read(pd);

mutex_lock(&file->mutex);
list_add_tail(&obj->uevent.uobject.list, &file->ucontext->qp_list);
@@ -1140,14 +1140,14 @@ err_destroy:
ib_destroy_qp(qp);

err_put:
- if (pd)
- put_pd_read(pd);
- if (scq)
- put_cq_read(scq);
- if (rcq && rcq != scq)
- put_cq_read(rcq);
if (srq)
put_srq_read(srq);
+ if (rcq && rcq != scq)
+ put_cq_read(rcq);
+ if (scq)
+ put_cq_read(scq);
+ if (pd)
+ put_pd_read(pd);

put_uobj_write(&obj->uevent.uobject);
return ret;
--
1.6.0.6


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