From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B98D47E for ; Sun, 22 Jan 2023 15:11:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3DE97C433EF; Sun, 22 Jan 2023 15:11:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1674400319; bh=LRp9/HvJhqNRzsDfyAIVIb42UnLc2RXTLgWhD5XWebo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cNpbVKloEz+o3LRx+Lk36dTKiZye32JeQwH0pbs+HWg7U1+ya0zn2MrjPHBPlDkJx P1tSh6XuF0qo52STAJMJgGD+NkeUUb6YPDEX/8xYMoGdf7X1yR56f9lAqxmpV48SE6 ZemoTAHF5yNquBMzLw0wPttbkUfF1wPoLav7E8+g= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Homin Rhee , Jens Axboe , Sasha Levin Subject: [PATCH 5.10 30/98] io_uring: ensure that cached task references are always put on exit Date: Sun, 22 Jan 2023 16:03:46 +0100 Message-Id: <20230122150230.744584618@linuxfoundation.org> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230122150229.351631432@linuxfoundation.org> References: <20230122150229.351631432@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Jens Axboe 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 Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- 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 -- 2.39.0