6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jens Axboe <axboe@xxxxxxxxx>
Commit c9a40292a44e78f71258b8522655bffaf5753bdb upstream.
io_eventfd_do_signal() is invoked from an RCU callback, but when
dropping the reference to the io_ev_fd, it calls io_eventfd_free()
directly if the refcount drops to zero. This isn't correct, as any
potential freeing of the io_ev_fd should be deferred another RCU grace
period.
Just call io_eventfd_put() rather than open-code the dec-and-test and
free, which will correctly defer it another RCU grace period.
Fixes: 21a091b970cd ("io_uring: signal registered eventfd to process deferred task work")
Reported-by: Jann Horn <jannh@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
io_uring/io_uring.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -479,6 +479,13 @@ static __cold void io_queue_deferred(str
}
}
+static void io_eventfd_free(struct rcu_head *rcu)
+{
+ struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu);
+
+ eventfd_ctx_put(ev_fd->cq_ev_fd);
+ kfree(ev_fd);
+}
static void io_eventfd_ops(struct rcu_head *rcu)
{
@@ -492,10 +499,8 @@ static void io_eventfd_ops(struct rcu_he
* ordering in a race but if references are 0 we know we have to free
* it regardless.
*/
- if (atomic_dec_and_test(&ev_fd->refs)) {
- eventfd_ctx_put(ev_fd->cq_ev_fd);
- kfree(ev_fd);
- }
+ if (atomic_dec_and_test(&ev_fd->refs))
+ call_rcu(&ev_fd->rcu, io_eventfd_free);
}
static void io_eventfd_signal(struct io_ring_ctx *ctx)
