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Date: Wed, 11 Mar 2026 09:06:36 -0600
From: Keith Busch <kbusch@kernel.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: io-uring@vger.kernel.org, asml.silence@gmail.com, naup96721@gmail.com,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/2] io_uring: ensure ctx->rings is stable for task work
 flags manipulation
Message-ID: <abGE_CLo4vW_-Tkh@kbusch-mbp>
References: <20260311131336.197028-1-axboe@kernel.dk>
 <20260311131336.197028-2-axboe@kernel.dk>
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In-Reply-To: <20260311131336.197028-2-axboe@kernel.dk>

On Wed, Mar 11, 2026 at 07:11:55AM -0600, Jens Axboe wrote:
> +/*
> + * Sets IORING_SQ_TASKRUN in the sq_flags shared with userspace, using the
> + * RCU protected rings pointer to be safe against concurrent ring resizing.
> + * Must be called inside an RCU read-side critical section.

You can make the rcu requirement explicit in the code with:

	ASSERT(rcu_read_lock_held());

And debug kernels will catch misuse, too.

> + */
> +static void io_ctx_mark_taskrun(struct io_ring_ctx *ctx)
> +{
> +	if (ctx->flags & IORING_SETUP_TASKRUN_FLAG) {
> +		struct io_rings *rings = rcu_dereference(ctx->rings_rcu);
> +
> +		atomic_or(IORING_SQ_TASKRUN, &rings->sq_flags);
> +	}
> +}