aio: kill the misleading rcu read locks in ioctx_add_table() and kill_ioctx()

ioctx_add_table() is the writer, it does not need rcu_read_lock() to
protect ->ioctx_table. It relies on mm->ioctx_lock and rcu locks just
add the confusion.

And it doesn't need rcu_dereference() by the same reason, it must see
any updates previously done under the same ->ioctx_lock. We could use
rcu_dereference_protected() but the patch uses rcu_dereference_raw(),
the function is simple enough.

The same for kill_ioctx(), although it does not update the pointer.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>

1 files changed, 3 insertions, 11 deletions

diff --git a/fs/aio.c b/fs/aio.c
index b6696462e345..c1d8c480c138 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -554,8 +554,7 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
         struct aio_ring *ring;
 
         spin_lock(&mm->ioctx_lock);
-        rcu_read_lock();
-        table = rcu_dereference(mm->ioctx_table);
+        table = rcu_dereference_raw(mm->ioctx_table);
 
         while (1) {
                 if (table)
@@ -563,7 +562,6 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
                                 if (!table->table[i]) {
                                         ctx->id = i;
                                         table->table[i] = ctx;
-                                        rcu_read_unlock();
                                         spin_unlock(&mm->ioctx_lock);
 
                                         /* While kioctx setup is in progress,
@@ -577,8 +575,6 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
                                 }
 
                 new_nr = (table ? table->nr : 1) * 4;
-
-                rcu_read_unlock();
                 spin_unlock(&mm->ioctx_lock);
 
                 table = kzalloc(sizeof(*table) + sizeof(struct kioctx *) *
@@ -589,8 +585,7 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
                 table->nr = new_nr;
 
                 spin_lock(&mm->ioctx_lock);
-                rcu_read_lock();
-                old = rcu_dereference(mm->ioctx_table);
+                old = rcu_dereference_raw(mm->ioctx_table);
 
                 if (!old) {
                         rcu_assign_pointer(mm->ioctx_table, table);
@@ -737,12 +732,9 @@ static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
 
 
         spin_lock(&mm->ioctx_lock);
-        rcu_read_lock();
-        table = rcu_dereference(mm->ioctx_table);
-
+        table = rcu_dereference_raw(mm->ioctx_table);
         WARN_ON(ctx != table->table[ctx->id]);
         table->table[ctx->id] = NULL;
-        rcu_read_unlock();
         spin_unlock(&mm->ioctx_lock);
 
         /* percpu_ref_kill() will do the necessary call_rcu() */