6.1-stable review patch. If anyone has any objections, please let me know.
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From: Jens Axboe axboe@kernel.dk
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@google.com Cc: stable@vger.kernel.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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)