Commit 855ef0de authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Benjamin LaHaise
Browse files

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: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarBenjamin LaHaise <bcrl@kvack.org>
parent 4b70ac5f

fs/aio.c

+3 −11
Original line number Diff line number Diff line
@@ -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() */

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