From nobody Fri Dec 19 17:34:20 2025 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 1961356475; Sun, 24 Mar 2024 22:35:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711319712; cv=none; b=Td3mNCAbxNHO0EfrIdUsZNOThBLSoot6MXJYU01hSBbiM3zbO7EJFwMJFvrB0hbKz0YVYd/TTCJZyA14okA/J3nIcFlfJIAFPXVDxDh02qSSSZ6h0ItUX4Noh9JS7pzygcgZ2OIWKS9KEoxySywF+Xbckkkv5Ad4dR5mkccJP4Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711319712; c=relaxed/simple; bh=RJktv4e4kUbn7b3tmJcoyfQyqcymeuVaVCsOQ4HQ5xg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OuaXJpy2otuma+aVndlyJb8E1XQwlzdJG+ObAf+QvQsqRYukhygcKIuthPzPgO4Vgg7FsP0zl60rVxhIaqhBPB+xOLJqEBm+RVFH0Gh5JjecB7L2egMJptCZ5uV5zQSzt8Nty9W64jIbpwggMV9qOpIwi68ctl2az57S3+dUQcg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BSfArjWM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BSfArjWM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0AABBC433A6; Sun, 24 Mar 2024 22:35:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711319711; bh=RJktv4e4kUbn7b3tmJcoyfQyqcymeuVaVCsOQ4HQ5xg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=BSfArjWMU03ioIvbig9Q4wjCfx6iPmZm3lk6IE5sSF9Rk1YJdyLrjRpKysfd3Gw0F 7jIVPcHbK57XmvDu72yr6b/7HaS6f8QhWXjfFRnq86TNECZ2cy2ijuUSC+BXXGCFOd dHOLFfLcm8V5eyOMC8HX9N8tlDWFRA2AbE8JuWHUhUD3t/ejAj62y4gv/MBzyql4L8 4nRMx+657dvIWmUokFcIbqWkBF+58ZByoRhQA++KDv4YmKtb0q272ce121Q3uX6oQd hGXuDDKbyXTF3pjwt0rIIsf6Fzk4VCicMyil9Ntp84qrnLRZjpExnr9TvQ7dQksb6z qj0FuNCfk5ROw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Jens Axboe , Sasha Levin Subject: [PATCH 6.8 014/715] io_uring: remove looping around handling traditional task_work Date: Sun, 24 Mar 2024 18:23:13 -0400 Message-ID: <20240324223455.1342824-15-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240324223455.1342824-1-sashal@kernel.org> References: <20240324223455.1342824-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Jens Axboe [ Upstream commit 592b4805432af075468876771c0f7d41273ccb3c ] A previous commit added looping around handling traditional task_work as an optimization, and while that may seem like a good idea, it's also possible to run into application starvation doing so. If the task_work generation is bursty, we can get very deep task_work queues, and we can end up looping in here for a very long time. One immediately observable problem with that is handling network traffic using provided buffers, where flooding incoming traffic and looping task_work handling will very quickly lead to buffer starvation as we keep running task_work rather than returning to the application so it can handle the associated CQEs and also provide buffers back. Fixes: 3a0c037b0e16 ("io_uring: batch task_work") Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- io_uring/io_uring.c | 45 +++++++-------------------------------------- 1 file changed, 7 insertions(+), 38 deletions(-) diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index cd9a137ad6cef..5233a20d01b54 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -1176,12 +1176,11 @@ static void ctx_flush_and_put(struct io_ring_ctx *c= tx, struct io_tw_state *ts) =20 static unsigned int handle_tw_list(struct llist_node *node, struct io_ring_ctx **ctx, - struct io_tw_state *ts, - struct llist_node *last) + struct io_tw_state *ts) { unsigned int count =3D 0; =20 - while (node && node !=3D last) { + do { struct llist_node *next =3D node->next; struct io_kiocb *req =3D container_of(node, struct io_kiocb, io_task_work.node); @@ -1205,7 +1204,7 @@ static unsigned int handle_tw_list(struct llist_node = *node, *ctx =3D NULL; cond_resched(); } - } + } while (node); =20 return count; } @@ -1224,22 +1223,6 @@ static inline struct llist_node *io_llist_xchg(struc= t llist_head *head, return xchg(&head->first, new); } =20 -/** - * io_llist_cmpxchg - possibly swap all entries in a lock-less list - * @head: the head of lock-less list to delete all entries - * @old: expected old value of the first entry of the list - * @new: new entry as the head of the list - * - * perform a cmpxchg on the first entry of the list. - */ - -static inline struct llist_node *io_llist_cmpxchg(struct llist_head *head, - struct llist_node *old, - struct llist_node *new) -{ - return cmpxchg(&head->first, old, new); -} - static __cold void io_fallback_tw(struct io_uring_task *tctx, bool sync) { struct llist_node *node =3D llist_del_all(&tctx->task_list); @@ -1274,9 +1257,7 @@ void tctx_task_work(struct callback_head *cb) struct io_ring_ctx *ctx =3D NULL; struct io_uring_task *tctx =3D container_of(cb, struct io_uring_task, task_work); - struct llist_node fake =3D {}; struct llist_node *node; - unsigned int loops =3D 0; unsigned int count =3D 0; =20 if (unlikely(current->flags & PF_EXITING)) { @@ -1284,21 +1265,9 @@ void tctx_task_work(struct callback_head *cb) return; } =20 - do { - loops++; - node =3D io_llist_xchg(&tctx->task_list, &fake); - count +=3D handle_tw_list(node, &ctx, &ts, &fake); - - /* skip expensive cmpxchg if there are items in the list */ - if (READ_ONCE(tctx->task_list.first) !=3D &fake) - continue; - if (ts.locked && !wq_list_empty(&ctx->submit_state.compl_reqs)) { - io_submit_flush_completions(ctx); - if (READ_ONCE(tctx->task_list.first) !=3D &fake) - continue; - } - node =3D io_llist_cmpxchg(&tctx->task_list, &fake, NULL); - } while (node !=3D &fake); + node =3D llist_del_all(&tctx->task_list); + if (node) + count =3D handle_tw_list(node, &ctx, &ts); =20 ctx_flush_and_put(ctx, &ts); =20 @@ -1306,7 +1275,7 @@ void tctx_task_work(struct callback_head *cb) if (unlikely(atomic_read(&tctx->in_cancel))) io_uring_drop_tctx_refs(current); =20 - trace_io_uring_task_work_run(tctx, count, loops); + trace_io_uring_task_work_run(tctx, count, 1); } =20 static inline void io_req_local_work_add(struct io_kiocb *req, unsigned fl= ags) --=20 2.43.0