genirq: Make sparse_irq_lock protect what it should protect

BugLink: http://bugs.launchpad.net/bugs/1721777
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 73be2b3909bd40a373e9c5237575faed5812945f..82afb7ed369f0df70bcd5d6fdc110addda5b842f 100644 (file)
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -421,10 +421,8 @@ static void free_desc(unsigned int irq)
         * The sysfs entry must be serialized against a concurrent
         * irq_sysfs_init() as well.
         */
-       mutex_lock(&sparse_irq_lock);
        kobject_del(&desc->kobj);
        delete_irq_desc(irq);
-       mutex_unlock(&sparse_irq_lock);
 
        /*
         * We free the descriptor, masks and stat fields via RCU. That
@@ -462,20 +460,15 @@ static int alloc_descs(unsigned int start, unsigned int cnt, int node,
                desc = alloc_desc(start + i, node, flags, mask, owner);
                if (!desc)
                        goto err;
-               mutex_lock(&sparse_irq_lock);
                irq_insert_desc(start + i, desc);
                irq_sysfs_add(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;
 }
 
@@ -575,6 +568,7 @@ static inline int alloc_descs(unsigned int start, unsigned int cnt, int node,
 
                desc->owner = owner;
        }
+       bitmap_set(allocated_irqs, start, cnt);
        return start;
 }
 
@@ -670,10 +664,10 @@ void irq_free_descs(unsigned int from, unsigned int cnt)
        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);
 }
@@ -720,19 +714,15 @@ __irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node,
                                           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, affinity, owner);
-
-err:
+       ret = alloc_descs(start, cnt, node, affinity, owner);
+unlock:
        mutex_unlock(&sparse_irq_lock);
        return ret;
 }