[PATCH] Convert idr's internal locking to _irqsave variant

Currently, the code in lib/idr.c uses a bare spin_lock(&idp->lock) to do
internal locking.  This is a nasty trap for code that might call idr
functions from different contexts; for example, it seems perfectly
reasonable to call idr_get_new() from process context and idr_remove() from
interrupt context -- but with the current locking this would lead to a
potential deadlock.

The simplest fix for this is to just convert the idr locking to use
spin_lock_irqsave().

In particular, this fixes a very complicated locking issue detected by
lockdep, involving the ib_ipoib driver's priv->lock and dev->_xmit_lock,
which get involved with the ib_sa module's query_idr.lock.

Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Zach Brown <zach.brown@oracle.com>,
Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 10 insertions, 6 deletions

diff --git a/lib/idr.c b/lib/idr.c
index 4d096819511a..16d2143fea48 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -38,14 +38,15 @@ static kmem_cache_t *idr_layer_cache;
 static struct idr_layer *alloc_layer(struct idr *idp)
 {
         struct idr_layer *p;
+        unsigned long flags;
 
-        spin_lock(&idp->lock);
+        spin_lock_irqsave(&idp->lock, flags);
         if ((p = idp->id_free)) {
                 idp->id_free = p->ary[0];
                 idp->id_free_cnt--;
                 p->ary[0] = NULL;
         }
-        spin_unlock(&idp->lock);
+        spin_unlock_irqrestore(&idp->lock, flags);
         return(p);
 }
 
@@ -59,12 +60,14 @@ static void __free_layer(struct idr *idp, struct idr_layer *p)
 
 static void free_layer(struct idr *idp, struct idr_layer *p)
 {
+        unsigned long flags;
+
         /*
          * Depends on the return element being zeroed.
          */
-        spin_lock(&idp->lock);
+        spin_lock_irqsave(&idp->lock, flags);
         __free_layer(idp, p);
-        spin_unlock(&idp->lock);
+        spin_unlock_irqrestore(&idp->lock, flags);
 }
 
 /**
@@ -168,6 +171,7 @@ static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
 {
         struct idr_layer *p, *new;
         int layers, v, id;
+        unsigned long flags;
 
         id = starting_id;
 build_up:
@@ -191,14 +195,14 @@ build_up:
                          * The allocation failed.  If we built part of
                          * the structure tear it down.
                          */
-                        spin_lock(&idp->lock);
+                        spin_lock_irqsave(&idp->lock, flags);
                         for (new = p; p && p != idp->top; new = p) {
                                 p = p->ary[0];
                                 new->ary[0] = NULL;
                                 new->bitmap = new->count = 0;
                                 __free_layer(idp, new);
                         }
-                        spin_unlock(&idp->lock);
+                        spin_unlock_irqrestore(&idp->lock, flags);
                         return -1;
                 }
                 new->ary[0] = p;