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 <o...@redhat.com>
---
fs/aio.c | 14 +++-----------
1 files changed, 3 insertions(+), 11 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index 3526c2b..a415870 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() */
--
1.5.5.1
--
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