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io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period

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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: 21a091b970 ("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>
This commit is contained in:
Jens Axboe
2025-01-08 11:16:13 -07:00
committed by Greg Kroah-Hartman
parent 03753bfacb
commit 8efff2aa2d
1 changed files with 9 additions and 4 deletions
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13
io_uring/io_uring.c
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@@ -537,6 +537,13 @@ static __cold void io_queue_deferred(struct io_ring_ctx *ctx)
}
}
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)
{
@@ -550,10 +557,8 @@ static void io_eventfd_ops(struct rcu_head *rcu)
* 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)