Commit 36f55889 authored by Kent Overstreet's avatar Kent Overstreet Committed by Linus Torvalds
Browse files

aio: refcounting cleanup



The usage of ctx->dead was fubar - it makes no sense to explicitly check
it all over the place, especially when we're already using RCU.

Now, ctx->dead only indicates whether we've dropped the initial
refcount. The new teardown sequence is:

  set ctx->dead
  hlist_del_rcu();
  synchronize_rcu();

Now we know no system calls can take a new ref, and it's safe to drop
the initial ref:

  put_ioctx();

We also need to ensure there are no more outstanding kiocbs.  This was
done incorrectly - it was being done in kill_ctx(), and before dropping
the initial refcount.  At this point, other syscalls may still be
submitting kiocbs!

Now, we cancel and wait for outstanding kiocbs in free_ioctx(), after
kioctx->users has dropped to 0 and we know no more iocbs could be
submitted.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: default avatarKent Overstreet <koverstreet@google.com>
Cc: Zach Brown <zab@redhat.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Asai Thambi S P <asamymuthupa@micron.com>
Cc: Selvan Mani <smani@micron.com>
Cc: Sam Bradshaw <sbradshaw@micron.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Reviewed-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 11599eba
......@@ -79,7 +79,7 @@ static inline unsigned aio_ring_avail(struct aio_ring_info *info,
struct kioctx {
atomic_t users;
int dead;
atomic_t dead;
/* This needs improving */
unsigned long user_id;
......@@ -98,6 +98,7 @@ struct kioctx {
struct aio_ring_info ring_info;
struct rcu_head rcu_head;
struct work_struct rcu_work;
};
/*------ sysctl variables----*/
......@@ -237,44 +238,6 @@ static int aio_setup_ring(struct kioctx *ctx)
kunmap_atomic((void *)((unsigned long)__event & PAGE_MASK)); \
} while(0)
static void ctx_rcu_free(struct rcu_head *head)
{
struct kioctx *ctx = container_of(head, struct kioctx, rcu_head);
kmem_cache_free(kioctx_cachep, ctx);
}
/* __put_ioctx
* Called when the last user of an aio context has gone away,
* and the struct needs to be freed.
*/
static void __put_ioctx(struct kioctx *ctx)
{
unsigned nr_events = ctx->max_reqs;
BUG_ON(atomic_read(&ctx->reqs_active));
aio_free_ring(ctx);
if (nr_events) {
spin_lock(&aio_nr_lock);
BUG_ON(aio_nr - nr_events > aio_nr);
aio_nr -= nr_events;
spin_unlock(&aio_nr_lock);
}
pr_debug("freeing %p\n", ctx);
call_rcu(&ctx->rcu_head, ctx_rcu_free);
}
static inline int try_get_ioctx(struct kioctx *kioctx)
{
return atomic_inc_not_zero(&kioctx->users);
}
static inline void put_ioctx(struct kioctx *kioctx)
{
BUG_ON(atomic_read(&kioctx->users) <= 0);
if (unlikely(atomic_dec_and_test(&kioctx->users)))
__put_ioctx(kioctx);
}
static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb,
struct io_event *res)
{
......@@ -298,6 +261,61 @@ static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb,
return ret;
}
static void free_ioctx_rcu(struct rcu_head *head)
{
struct kioctx *ctx = container_of(head, struct kioctx, rcu_head);
kmem_cache_free(kioctx_cachep, ctx);
}
/*
* When this function runs, the kioctx has been removed from the "hash table"
* and ctx->users has dropped to 0, so we know no more kiocbs can be submitted -
* now it's safe to cancel any that need to be.
*/
static void free_ioctx(struct kioctx *ctx)
{
struct io_event res;
struct kiocb *req;
spin_lock_irq(&ctx->ctx_lock);
while (!list_empty(&ctx->active_reqs)) {
req = list_first_entry(&ctx->active_reqs,
struct kiocb, ki_list);
list_del_init(&req->ki_list);
kiocb_cancel(ctx, req, &res);
}
spin_unlock_irq(&ctx->ctx_lock);
wait_event(ctx->wait, !atomic_read(&ctx->reqs_active));
aio_free_ring(ctx);
spin_lock(&aio_nr_lock);
BUG_ON(aio_nr - ctx->max_reqs > aio_nr);
aio_nr -= ctx->max_reqs;
spin_unlock(&aio_nr_lock);
pr_debug("freeing %p\n", ctx);
/*
* Here the call_rcu() is between the wait_event() for reqs_active to
* hit 0, and freeing the ioctx.
*
* aio_complete() decrements reqs_active, but it has to touch the ioctx
* after to issue a wakeup so we use rcu.
*/
call_rcu(&ctx->rcu_head, free_ioctx_rcu);
}
static void put_ioctx(struct kioctx *ctx)
{
if (unlikely(atomic_dec_and_test(&ctx->users)))
free_ioctx(ctx);
}
/* ioctx_alloc
* Allocates and initializes an ioctx. Returns an ERR_PTR if it failed.
*/
......@@ -324,6 +342,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
ctx->max_reqs = nr_events;
atomic_set(&ctx->users, 2);
atomic_set(&ctx->dead, 0);
spin_lock_init(&ctx->ctx_lock);
spin_lock_init(&ctx->ring_info.ring_lock);
init_waitqueue_head(&ctx->wait);
......@@ -361,44 +380,43 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
return ERR_PTR(err);
}
/* kill_ctx
* Cancels all outstanding aio requests on an aio context. Used
* when the processes owning a context have all exited to encourage
* the rapid destruction of the kioctx.
*/
static void kill_ctx(struct kioctx *ctx)
static void kill_ioctx_work(struct work_struct *work)
{
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
struct io_event res;
struct kiocb *req;
struct kioctx *ctx = container_of(work, struct kioctx, rcu_work);
spin_lock_irq(&ctx->ctx_lock);
ctx->dead = 1;
while (!list_empty(&ctx->active_reqs)) {
req = list_first_entry(&ctx->active_reqs,
struct kiocb, ki_list);
wake_up_all(&ctx->wait);
put_ioctx(ctx);
}
list_del_init(&req->ki_list);
kiocb_cancel(ctx, req, &res);
}
static void kill_ioctx_rcu(struct rcu_head *head)
{
struct kioctx *ctx = container_of(head, struct kioctx, rcu_head);
if (!atomic_read(&ctx->reqs_active))
goto out;
INIT_WORK(&ctx->rcu_work, kill_ioctx_work);
schedule_work(&ctx->rcu_work);
}
add_wait_queue(&ctx->wait, &wait);
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
while (atomic_read(&ctx->reqs_active)) {
spin_unlock_irq(&ctx->ctx_lock);
io_schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
spin_lock_irq(&ctx->ctx_lock);
}
__set_task_state(tsk, TASK_RUNNING);
remove_wait_queue(&ctx->wait, &wait);
/* kill_ioctx
* Cancels all outstanding aio requests on an aio context. Used
* when the processes owning a context have all exited to encourage
* the rapid destruction of the kioctx.
*/
static void kill_ioctx(struct kioctx *ctx)
{
if (!atomic_xchg(&ctx->dead, 1)) {
hlist_del_rcu(&ctx->list);
/* Between hlist_del_rcu() and dropping the initial ref */
synchronize_rcu();
out:
spin_unlock_irq(&ctx->ctx_lock);
/*
* We can't punt to workqueue here because put_ioctx() ->
* free_ioctx() will unmap the ringbuffer, and that has to be
* done in the original process's context. kill_ioctx_rcu/work()
* exist for exit_aio(), as in that path free_ioctx() won't do
* the unmap.
*/
kill_ioctx_work(&ctx->rcu_work);
}
}
/* wait_on_sync_kiocb:
......@@ -417,27 +435,25 @@ ssize_t wait_on_sync_kiocb(struct kiocb *iocb)
}
EXPORT_SYMBOL(wait_on_sync_kiocb);
/* exit_aio: called when the last user of mm goes away. At this point,
* there is no way for any new requests to be submited or any of the
* io_* syscalls to be called on the context. However, there may be
* outstanding requests which hold references to the context; as they
* go away, they will call put_ioctx and release any pinned memory
* associated with the request (held via struct page * references).
/*
* exit_aio: called when the last user of mm goes away. At this point, there is
* no way for any new requests to be submited or any of the io_* syscalls to be
* called on the context.
*
* There may be outstanding kiocbs, but free_ioctx() will explicitly wait on
* them.
*/
void exit_aio(struct mm_struct *mm)
{
struct kioctx *ctx;
struct hlist_node *n;
while (!hlist_empty(&mm->ioctx_list)) {
ctx = hlist_entry(mm->ioctx_list.first, struct kioctx, list);
hlist_del_rcu(&ctx->list);
kill_ctx(ctx);
hlist_for_each_entry_safe(ctx, n, &mm->ioctx_list, list) {
if (1 != atomic_read(&ctx->users))
printk(KERN_DEBUG
"exit_aio:ioctx still alive: %d %d %d\n",
atomic_read(&ctx->users), ctx->dead,
atomic_read(&ctx->users),
atomic_read(&ctx->dead),
atomic_read(&ctx->reqs_active));
/*
* We don't need to bother with munmap() here -
......@@ -448,7 +464,11 @@ void exit_aio(struct mm_struct *mm)
* place that uses ->mmap_size, so it's safe.
*/
ctx->ring_info.mmap_size = 0;
put_ioctx(ctx);
if (!atomic_xchg(&ctx->dead, 1)) {
hlist_del_rcu(&ctx->list);
call_rcu(&ctx->rcu_head, kill_ioctx_rcu);
}
}
}
......@@ -514,8 +534,6 @@ static void kiocb_batch_free(struct kioctx *ctx, struct kiocb_batch *batch)
kmem_cache_free(kiocb_cachep, req);
atomic_dec(&ctx->reqs_active);
}
if (unlikely(!atomic_read(&ctx->reqs_active) && ctx->dead))
wake_up_all(&ctx->wait);
spin_unlock_irq(&ctx->ctx_lock);
}
......@@ -612,13 +630,8 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
rcu_read_lock();
hlist_for_each_entry_rcu(ctx, &mm->ioctx_list, list) {
/*
* RCU protects us against accessing freed memory but
* we have to be careful not to get a reference when the
* reference count already dropped to 0 (ctx->dead test
* is unreliable because of races).
*/
if (ctx->user_id == ctx_id && !ctx->dead && try_get_ioctx(ctx)){
if (ctx->user_id == ctx_id) {
atomic_inc(&ctx->users);
ret = ctx;
break;
}
......@@ -657,12 +670,15 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
info = &ctx->ring_info;
/* add a completion event to the ring buffer.
* must be done holding ctx->ctx_lock to prevent
* other code from messing with the tail
* pointer since we might be called from irq
* context.
/*
* Add a completion event to the ring buffer. Must be done holding
* ctx->ctx_lock to prevent other code from messing with the tail
* pointer since we might be called from irq context.
*
* Take rcu_read_lock() in case the kioctx is being destroyed, as we
* need to issue a wakeup after decrementing reqs_active.
*/
rcu_read_lock();
spin_lock_irqsave(&ctx->ctx_lock, flags);
list_del(&iocb->ki_list); /* remove from active_reqs */
......@@ -728,6 +744,7 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
wake_up(&ctx->wait);
spin_unlock_irqrestore(&ctx->ctx_lock, flags);
rcu_read_unlock();
}
EXPORT_SYMBOL(aio_complete);
......@@ -871,7 +888,7 @@ static int read_events(struct kioctx *ctx,
break;
if (min_nr <= i)
break;
if (unlikely(ctx->dead)) {
if (unlikely(atomic_read(&ctx->dead))) {
ret = -EINVAL;
break;
}
......@@ -914,35 +931,6 @@ static int read_events(struct kioctx *ctx,
return i ? i : ret;
}
/* Take an ioctx and remove it from the list of ioctx's. Protects
* against races with itself via ->dead.
*/
static void io_destroy(struct kioctx *ioctx)
{
struct mm_struct *mm = current->mm;
int was_dead;
/* delete the entry from the list is someone else hasn't already */
spin_lock(&mm->ioctx_lock);
was_dead = ioctx->dead;
ioctx->dead = 1;
hlist_del_rcu(&ioctx->list);
spin_unlock(&mm->ioctx_lock);
pr_debug("(%p)\n", ioctx);
if (likely(!was_dead))
put_ioctx(ioctx); /* twice for the list */
kill_ctx(ioctx);
/*
* Wake up any waiters. The setting of ctx->dead must be seen
* by other CPUs at this point. Right now, we rely on the
* locking done by the above calls to ensure this consistency.
*/
wake_up_all(&ioctx->wait);
}
/* sys_io_setup:
* Create an aio_context capable of receiving at least nr_events.
* ctxp must not point to an aio_context that already exists, and
......@@ -978,7 +966,7 @@ SYSCALL_DEFINE2(io_setup, unsigned, nr_events, aio_context_t __user *, ctxp)
if (!IS_ERR(ioctx)) {
ret = put_user(ioctx->user_id, ctxp);
if (ret)
io_destroy(ioctx);
kill_ioctx(ioctx);
put_ioctx(ioctx);
}
......@@ -996,7 +984,7 @@ SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)
{
struct kioctx *ioctx = lookup_ioctx(ctx);
if (likely(NULL != ioctx)) {
io_destroy(ioctx);
kill_ioctx(ioctx);
put_ioctx(ioctx);
return 0;
}
......@@ -1300,25 +1288,6 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
ret = aio_setup_iocb(req, compat);
if (ret)
goto out_put_req;
spin_lock_irq(&ctx->ctx_lock);
/*
* We could have raced with io_destroy() and are currently holding a
* reference to ctx which should be destroyed. We cannot submit IO
* since ctx gets freed as soon as io_submit() puts its reference. The
* check here is reliable: io_destroy() sets ctx->dead before waiting
* for outstanding IO and the barrier between these two is realized by
* unlock of mm->ioctx_lock and lock of ctx->ctx_lock. Analogously we
* increment ctx->reqs_active before checking for ctx->dead and the
* barrier is realized by unlock and lock of ctx->ctx_lock. Thus if we
* don't see ctx->dead set here, io_destroy() waits for our IO to
* finish.
*/
if (ctx->dead)
ret = -EINVAL;
spin_unlock_irq(&ctx->ctx_lock);
if (ret)
goto out_put_req;
......@@ -1348,9 +1317,6 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
spin_unlock_irq(&ctx->ctx_lock);
atomic_dec(&ctx->reqs_active);
if (unlikely(!atomic_read(&ctx->reqs_active) && ctx->dead))
wake_up_all(&ctx->wait);
aio_put_req(req); /* drop extra ref to req */
aio_put_req(req); /* drop i/o ref to req */
return ret;
......
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