1 files changed, 41 insertions, 11 deletions

diff --git a/fs/aio.c b/fs/aio.c
index fc557a3be0a9..26869cde3953 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -239,15 +239,23 @@ static void __put_ioctx(struct kioctx *ctx)
         call_rcu(&ctx->rcu_head, ctx_rcu_free);
 }
 
-#define get_ioctx(kioctx) do {                                          \
-        BUG_ON(atomic_read(&(kioctx)->users) <= 0);                     \
-        atomic_inc(&(kioctx)->users);                                   \
-} while (0)
-#define put_ioctx(kioctx) do {                                          \
-        BUG_ON(atomic_read(&(kioctx)->users) <= 0);                     \
-        if (unlikely(atomic_dec_and_test(&(kioctx)->users)))            \
-                __put_ioctx(kioctx);                                    \
-} while (0)
+static inline void get_ioctx(struct kioctx *kioctx)
+{
+        BUG_ON(atomic_read(&kioctx->users) <= 0);
+        atomic_inc(&kioctx->users);
+}
+
+static inline int try_get_ioctx(struct kioctx *kioctx)
+{
+        return atomic_inc_not_zero(&kioctx->users);
+}
+
+static inline void put_ioctx(struct kioctx *kioctx)
+{
+        BUG_ON(atomic_read(&kioctx->users) <= 0);
+        if (unlikely(atomic_dec_and_test(&kioctx->users)))
+                __put_ioctx(kioctx);
+}
 
 /* ioctx_alloc
  *      Allocates and initializes an ioctx.  Returns an ERR_PTR if it failed.
@@ -601,8 +609,13 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
         rcu_read_lock();
 
         hlist_for_each_entry_rcu(ctx, n, &mm->ioctx_list, list) {
-                if (ctx->user_id == ctx_id && !ctx->dead) {
-                        get_ioctx(ctx);
+                /*
+                 * RCU protects us against accessing freed memory but
+                 * we have to be careful not to get a reference when the
+                 * reference count already dropped to 0 (ctx->dead test
+                 * is unreliable because of races).
+                 */
+                if (ctx->user_id == ctx_id && !ctx->dead && try_get_ioctx(ctx)){
                         ret = ctx;
                         break;
                 }
@@ -1629,6 +1642,23 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
                 goto out_put_req;
 
         spin_lock_irq(&ctx->ctx_lock);
+        /*
+         * We could have raced with io_destroy() and are currently holding a
+         * reference to ctx which should be destroyed. We cannot submit IO
+         * since ctx gets freed as soon as io_submit() puts its reference.  The
+         * check here is reliable: io_destroy() sets ctx->dead before waiting
+         * for outstanding IO and the barrier between these two is realized by
+         * unlock of mm->ioctx_lock and lock of ctx->ctx_lock.  Analogously we
+         * increment ctx->reqs_active before checking for ctx->dead and the
+         * barrier is realized by unlock and lock of ctx->ctx_lock. Thus if we
+         * don't see ctx->dead set here, io_destroy() waits for our IO to
+         * finish.
+         */
+        if (ctx->dead) {
+                spin_unlock_irq(&ctx->ctx_lock);
+                ret = -EINVAL;
+                goto out_put_req;
+        }
         aio_run_iocb(req);
         if (!list_empty(&ctx->run_list)) {
                 /* drain the run list */