aio: report error from io_destroy() when threads race in io_destroy()

As reported by Anatol Pomozov, io_destroy() fails to report an error when
it loses the race to destroy a given ioctx.  Since there is a difference in
behaviour between the thread that wins the race (which blocks on outstanding
io requests) versus lthe thread that loses (which returns immediately), wire
up a return code from kill_ioctx() to the io_destroy() syscall.

Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
Cc: Anatol Pomozov <anatol.pomozov@gmail.com>

1 files changed, 9 insertions, 7 deletions

diff --git a/fs/aio.c b/fs/aio.c
index 908006e8c7ff..044c1c86decc 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -727,7 +727,7 @@ err:
  *      when the processes owning a context have all exited to encourage
  *      the rapid destruction of the kioctx.
  */
-static void kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
+static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
                 struct completion *requests_done)
 {
         if (!atomic_xchg(&ctx->dead, 1)) {
@@ -759,10 +759,10 @@ static void kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
 
                 ctx->requests_done = requests_done;
                 percpu_ref_kill(&ctx->users);
-        } else {
-                if (requests_done)
-                        complete(requests_done);
+                return 0;
         }
+
+        return -EINVAL;
 }
 
 /* wait_on_sync_kiocb:
@@ -1219,21 +1219,23 @@ SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)
         if (likely(NULL != ioctx)) {
                 struct completion requests_done =
                         COMPLETION_INITIALIZER_ONSTACK(requests_done);
+                int ret;
 
                 /* Pass requests_done to kill_ioctx() where it can be set
                  * in a thread-safe way. If we try to set it here then we have
                  * a race condition if two io_destroy() called simultaneously.
                  */
-                kill_ioctx(current->mm, ioctx, &requests_done);
+                ret = kill_ioctx(current->mm, ioctx, &requests_done);
                 percpu_ref_put(&ioctx->users);
 
                 /* Wait until all IO for the context are done. Otherwise kernel
                  * keep using user-space buffers even if user thinks the context
                  * is destroyed.
                  */
-                wait_for_completion(&requests_done);
+                if (!ret)
+                        wait_for_completion(&requests_done);
 
-                return 0;
+                return ret;
         }
         pr_debug("EINVAL: io_destroy: invalid context id\n");
         return -EINVAL;