[PATCH 3.2 41/61] genirq: Make sparse_irq_lock protect what it should protect

[Ben Hutchings <ben@decadent.org.uk>]

3.2.96-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@linutronix.de>

commit 12ac1d0f6c3e95732d144ffa65c8b20fbd9aa462 upstream.

for_each_active_irq() iterates the sparse irq allocation bitmap. The caller
must hold sparse_irq_lock. Several code pathes expect that an active bit in
the sparse bitmap also has a valid interrupt descriptor.

Unfortunately that's not true. The (de)allocation is a two step process,
which holds the sparse_irq_lock only across the queue/remove from the radix
tree and the set/clear in the allocation bitmap.

If a iteration locks sparse_irq_lock between the two steps, then it might
see an active bit but the corresponding irq descriptor is NULL. If that is
dereferenced unconditionally, then the kernel oopses. Of course, all
iterator sites could be audited and fixed, but....

There is no reason why the sparse_irq_lock needs to be dropped between the
two steps, in fact the code becomes simpler when the mutex is held across
both and the semantics become more straight forward, so future problems of
missing NULL pointer checks in the iteration are avoided and all existing
sites are fixed in one go.

Expand the lock held sections so both operations are covered and the bitmap
and the radixtree are in sync.

Fixes: a05a900a51c7 ("genirq: Make sparse_lock a mutex")
Reported-and-tested-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 kernel/irq/irqdesc.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -182,9 +182,7 @@ static void free_desc(unsigned int irq)
 	 * sparse tree we can free it. Access in proc will fail to
 	 * lookup the descriptor.
 	 */
-	mutex_lock(&sparse_irq_lock);
 	delete_irq_desc(irq);
-	mutex_unlock(&sparse_irq_lock);
 
 	free_masks(desc);
 	free_percpu(desc->kstat_irqs);
@@ -201,19 +199,14 @@ static int alloc_descs(unsigned int star
 		desc = alloc_desc(start + i, node, owner);
 		if (!desc)
 			goto err;
-		mutex_lock(&sparse_irq_lock);
 		irq_insert_desc(start + i, desc);
-		mutex_unlock(&sparse_irq_lock);
 	}
+	bitmap_set(allocated_irqs, start, cnt);
 	return start;
 
 err:
 	for (i--; i >= 0; i--)
 		free_desc(start + i);
-
-	mutex_lock(&sparse_irq_lock);
-	bitmap_clear(allocated_irqs, start, cnt);
-	mutex_unlock(&sparse_irq_lock);
 	return -ENOMEM;
 }
 
@@ -305,6 +298,7 @@ static inline int alloc_descs(unsigned i
 
 		desc->owner = owner;
 	}
+	bitmap_set(allocated_irqs, start, cnt);
 	return start;
 }
 
@@ -345,10 +339,10 @@ void irq_free_descs(unsigned int from, u
 	if (from >= nr_irqs || (from + cnt) > nr_irqs)
 		return;
 
+	mutex_lock(&sparse_irq_lock);
 	for (i = 0; i < cnt; i++)
 		free_desc(from + i);
 
-	mutex_lock(&sparse_irq_lock);
 	bitmap_clear(allocated_irqs, from, cnt);
 	mutex_unlock(&sparse_irq_lock);
 }
@@ -385,19 +379,15 @@ __irq_alloc_descs(int irq, unsigned int
 					   from, cnt, 0);
 	ret = -EEXIST;
 	if (irq >=0 && start != irq)
-		goto err;
+		goto unlock;
 
 	if (start + cnt > nr_irqs) {
 		ret = irq_expand_nr_irqs(start + cnt);
 		if (ret)
-			goto err;
+			goto unlock;
 	}
-
-	bitmap_set(allocated_irqs, start, cnt);
-	mutex_unlock(&sparse_irq_lock);
-	return alloc_descs(start, cnt, node, owner);
-
-err:
+	ret = alloc_descs(start, cnt, node, owner);
+unlock:
 	mutex_unlock(&sparse_irq_lock);
 	return ret;
 }