make vfree() safe to call from interrupt contexts

A bunch of RCU callbacks want to be able to do vfree() and end up with
rather kludgy schemes.  Just let vfree() do the right thing - put the
victim on llist and schedule actual __vunmap() via schedule_work(), so
that it runs from non-interrupt context.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 40 insertions, 5 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 0f751f2068c3..ef9bdf742273 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -27,10 +27,30 @@
 #include <linux/pfn.h>
 #include <linux/kmemleak.h>
 #include <linux/atomic.h>
+#include <linux/llist.h>
 #include <asm/uaccess.h>
 #include <asm/tlbflush.h>
 #include <asm/shmparam.h>
 
+struct vfree_deferred {
+        struct llist_head list;
+        struct work_struct wq;
+};
+static DEFINE_PER_CPU(struct vfree_deferred, vfree_deferred);
+
+static void __vunmap(const void *, int);
+
+static void free_work(struct work_struct *w)
+{
+        struct vfree_deferred *p = container_of(w, struct vfree_deferred, wq);
+        struct llist_node *llnode = llist_del_all(&p->list);
+        while (llnode) {
+                void *p = llnode;
+                llnode = llist_next(llnode);
+                __vunmap(p, 1);
+        }
+}
+
 /*** Page table manipulation functions ***/
 
 static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end)
@@ -1184,10 +1204,14 @@ void __init vmalloc_init(void)
 
         for_each_possible_cpu(i) {
                 struct vmap_block_queue *vbq;
+                struct vfree_deferred *p;
 
                 vbq = &per_cpu(vmap_block_queue, i);
                 spin_lock_init(&vbq->lock);
                 INIT_LIST_HEAD(&vbq->free);
+                p = &per_cpu(vfree_deferred, i);
+                init_llist_head(&p->list);
+                INIT_WORK(&p->wq, free_work);
         }
 
         /* Import existing vmlist entries. */
@@ -1511,7 +1535,7 @@ static void __vunmap(const void *addr, int deallocate_pages)
         kfree(area);
         return;
 }
-
+ 
 /**
  *      vfree  -  release memory allocated by vmalloc()
  *      @addr:          memory base address
@@ -1520,15 +1544,25 @@ static void __vunmap(const void *addr, int deallocate_pages)
  *      obtained from vmalloc(), vmalloc_32() or __vmalloc(). If @addr is
  *      NULL, no operation is performed.
  *
- *      Must not be called in interrupt context.
+ *      Must not be called in NMI context (strictly speaking, only if we don't
+ *      have CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG, but making the calling
+ *      conventions for vfree() arch-depenedent would be a really bad idea)
+ *      
  */
 void vfree(const void *addr)
 {
-        BUG_ON(in_interrupt());
+        BUG_ON(in_nmi());
 
         kmemleak_free(addr);
 
-        __vunmap(addr, 1);
+        if (!addr)
+                return;
+        if (unlikely(in_interrupt())) {
+                struct vfree_deferred *p = &__get_cpu_var(vfree_deferred);
+                llist_add((struct llist_node *)addr, &p->list);
+                schedule_work(&p->wq);
+        } else
+                __vunmap(addr, 1);
 }
 EXPORT_SYMBOL(vfree);
 
@@ -1545,7 +1579,8 @@ void vunmap(const void *addr)
 {
         BUG_ON(in_interrupt());
         might_sleep();
-        __vunmap(addr, 0);
+        if (addr)
+                __vunmap(addr, 0);
 }
 EXPORT_SYMBOL(vunmap);