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

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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>
This commit is contained in:
Oleg Nesterov 2014-04-30 16:16:36 +02:00 committed by Benjamin LaHaise
parent 4b70ac5fd9
commit 855ef0dec7
1 changed files with 3 additions and 11 deletions
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14
fs/aio.c
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@ -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() */