Merge branch 'mlog_replace_for_39' of git://repo.or.cz/taoma-kernel into ocfs2-merge-window-fix

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 */