From: Jens Axboe axboe@kernel.dk
commit e775f93f2ab976a2cdb4a7b53063cbe890904f73 upstream.
io_uring caches task references to avoid doing atomics for each of them per request. If a request is put from the same task that allocated it, then we can maintain a per-ctx cache of them. This obviously relies on io_uring always pruning caches in a reliable way, and there's currently a case off io_uring fd release where we can miss that.
One example is a ring setup with IOPOLL, which relies on the task polling for completions, which will free them. However, if such a task submits a request and then exits or closes the ring without reaping the completion, then ring release will reap and put. If release happens from that very same task, the completed request task refs will get put back into the cache pool. This is problematic, as we're now beyond the point of pruning caches.
Manually drop these caches after doing an IOPOLL reap. This releases references from the current task, which is enough. If another task happens to be doing the release, then the caching will not be triggered and there's no issue.
Cc: stable@vger.kernel.org Fixes: e98e49b2bbf7 ("io_uring: extend task put optimisations") Reported-by: Homin Rhee hominlab@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- io_uring/io_uring.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index e8852d56b1ec..f8a0d228d799 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -9513,6 +9513,10 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx) /* if we failed setting up the ctx, we might not have any rings */ io_iopoll_try_reap_events(ctx);
+ /* drop cached put refs after potentially doing completions */ + if (current->io_uring) + io_uring_drop_tctx_refs(current); + INIT_WORK(&ctx->exit_work, io_ring_exit_work); /* * Use system_unbound_wq to avoid spawning tons of event kworkers