This is needed to prevent races caused by the way the ->poll API works.
To avoid introducing overhead for other users of the iocbs we initialize
it to zero and only do refcount operations if it is non-zero in the
completion path.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
fs/aio.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index 27454594e37a..7f3c159b3e2e 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -178,6 +178,7 @@ struct aio_kiocb {
struct list_head ki_list; /* the aio core uses this
* for cancellation */
+ atomic_t ki_refcnt;
/*
* If the aio_resfd field of the userspace iocb is not zero,
@@ -1015,6 +1016,7 @@ static inline struct aio_kiocb *aio_get_req(struct kioctx *ctx)
percpu_ref_get(&ctx->reqs);
INIT_LIST_HEAD(&req->ki_list);
+ atomic_set(&req->ki_refcnt, 0);
req->ki_ctx = ctx;
return req;
out_put:
@@ -1049,6 +1051,15 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
return ret;
}
+static inline void iocb_put(struct aio_kiocb *iocb)
+{
+ if (atomic_read(&iocb->ki_refcnt) == 0 ||
+ atomic_dec_and_test(&iocb->ki_refcnt)) {
+ percpu_ref_put(&iocb->ki_ctx->reqs);
+ kmem_cache_free(kiocb_cachep, iocb);
+ }
+}
+
/* aio_complete
* Called when the io request on the given iocb is complete.
*/
@@ -1118,8 +1129,6 @@ static void aio_complete(struct aio_kiocb *iocb, long res, long res2)
eventfd_ctx_put(iocb->ki_eventfd);
}
- kmem_cache_free(kiocb_cachep, iocb);
-
/*
* We have to order our ring_info tail store above and test
* of the wait list below outside the wait lock. This is
@@ -1130,8 +1139,7 @@ static void aio_complete(struct aio_kiocb *iocb, long res, long res2)
if (waitqueue_active(&ctx->wait))
wake_up(&ctx->wait);
-
- percpu_ref_put(&ctx->reqs);
+ iocb_put(iocb);
}
/* aio_read_events_ring
--
2.18.0
