[PATCH 07/36] aio: add delayed cancel support

Christoph Hellwig
2018-03-05T21:43:43Z

The upcoming aio poll support would like to be able to complete the
iocb inline from the cancellation context, but that would cause
a lock order reversal. Add support for optionally moving the cancelation
outside the context lock to avoid this reversal.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
---
fs/aio.c | 49 ++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 38 insertions(+), 11 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 0b6394b4e528..9d7d6e4cde87 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -170,6 +170,10 @@ struct aio_kiocb {
struct list_head ki_list; /* the aio core uses this
* for cancellation */

+ unsigned int flags; /* protected by ctx->ctx_lock */
+#define AIO_IOCB_DELAYED_CANCEL (1 << 0)
+#define AIO_IOCB_CANCELLED (1 << 1)
+
/*
* If the aio_resfd field of the userspace iocb is not zero,
* this is the underlying eventfd context to deliver events to.
@@ -536,9 +540,9 @@ static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
#define AIO_EVENTS_FIRST_PAGE ((PAGE_SIZE - sizeof(struct aio_ring)) / sizeof(struct io_event))
#define AIO_EVENTS_OFFSET (AIO_EVENTS_PER_PAGE - AIO_EVENTS_FIRST_PAGE)

-void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
+static void __kiocb_set_cancel_fn(struct aio_kiocb *req,
+ kiocb_cancel_fn *cancel, unsigned int iocb_flags)
{
- struct aio_kiocb *req = container_of(iocb, struct aio_kiocb, rw);
struct kioctx *ctx = req->ki_ctx;
unsigned long flags;

@@ -548,8 +552,15 @@ void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
spin_lock_irqsave(&ctx->ctx_lock, flags);
list_add_tail(&req->ki_list, &ctx->active_reqs);
req->ki_cancel = cancel;
+ req->flags |= iocb_flags;
spin_unlock_irqrestore(&ctx->ctx_lock, flags);
}
+
+void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
+{
+ return __kiocb_set_cancel_fn(container_of(iocb, struct aio_kiocb, rw),
+ cancel, 0);
+}
EXPORT_SYMBOL(kiocb_set_cancel_fn);

/*
@@ -603,17 +614,27 @@ static void free_ioctx_users(struct percpu_ref *ref)
{
struct kioctx *ctx = container_of(ref, struct kioctx, users);
struct aio_kiocb *req;
+ LIST_HEAD(list);

spin_lock_irq(&ctx->ctx_lock);
-
while (!list_empty(&ctx->active_reqs)) {
req = list_first_entry(&ctx->active_reqs,
struct aio_kiocb, ki_list);
- kiocb_cancel(req);
- }

+ if (req->flags & AIO_IOCB_DELAYED_CANCEL) {
+ req->flags |= AIO_IOCB_CANCELLED;
+ list_move_tail(&req->ki_list, &list);
+ } else {
+ kiocb_cancel(req);
+ }
+ }
spin_unlock_irq(&ctx->ctx_lock);

+ while (!list_empty(&list)) {
+ req = list_first_entry(&list, struct aio_kiocb, ki_list);
+ kiocb_cancel(req);
+ }
+
percpu_ref_kill(&ctx->reqs);
percpu_ref_put(&ctx->reqs);
}
@@ -1785,15 +1806,22 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
if (unlikely(!ctx))
return -EINVAL;

- spin_lock_irq(&ctx->ctx_lock);
+ ret = -EINVAL;

+ spin_lock_irq(&ctx->ctx_lock);
kiocb = lookup_kiocb(ctx, iocb, key);
+ if (kiocb) {
+ if (kiocb->flags & AIO_IOCB_DELAYED_CANCEL) {
+ kiocb->flags |= AIO_IOCB_CANCELLED;
+ } else {
+ ret = kiocb_cancel(kiocb);
+ kiocb = NULL;
+ }
+ }
+ spin_unlock_irq(&ctx->ctx_lock);
+
if (kiocb)
ret = kiocb_cancel(kiocb);
- else
- ret = -EINVAL;
-
- spin_unlock_irq(&ctx->ctx_lock);

if (!ret) {
/*
@@ -1805,7 +1833,6 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
}

percpu_ref_put(&ctx->users);
-
return ret;
}

--
2.14.2