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From:   Usama Arif <usama.arif@bytedance.com>
To:     io-uring@vger.kernel.org, axboe@kernel.dk, asml.silence@gmail.com,
        linux-kernel@vger.kernel.org
Cc:     fam.zheng@bytedance.com, Usama Arif <usama.arif@bytedance.com>
Subject: [PATCH v5 4/4] io_uring: remove ring quiesce for io_uring_register
Date:   Thu,  3 Feb 2022 23:34:39 +0000
Message-Id: <20220203233439.845408-5-usama.arif@bytedance.com>
In-Reply-To: <20220203233439.845408-1-usama.arif@bytedance.com>
References: <20220203233439.845408-1-usama.arif@bytedance.com>
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Ring quiesce is currently only used for 2 opcodes
IORING_REGISTER_ENABLE_RINGS and IORING_REGISTER_RESTRICTIONS.
IORING_SETUP_R_DISABLED prevents submitting requests and
so there will be no requests until IORING_REGISTER_ENABLE_RINGS
is called. And IORING_REGISTER_RESTRICTIONS works only before
IORING_REGISTER_ENABLE_RINGS is called. Hence ring quiesce is
not needed for these opcodes and therefore io_uring_register.

Signed-off-by: Usama Arif <usama.arif@bytedance.com>
---
 fs/io_uring.c | 69 ---------------------------------------------------
 1 file changed, 69 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5ae51ea12f0f..89e4dd7e8995 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -11022,64 +11022,6 @@ static __cold int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 	return ret;
 }
 
-static bool io_register_op_must_quiesce(int op)
-{
-	switch (op) {
-	case IORING_REGISTER_BUFFERS:
-	case IORING_UNREGISTER_BUFFERS:
-	case IORING_REGISTER_FILES:
-	case IORING_UNREGISTER_FILES:
-	case IORING_REGISTER_FILES_UPDATE:
-	case IORING_REGISTER_EVENTFD:
-	case IORING_REGISTER_EVENTFD_ASYNC:
-	case IORING_UNREGISTER_EVENTFD:
-	case IORING_REGISTER_PROBE:
-	case IORING_REGISTER_PERSONALITY:
-	case IORING_UNREGISTER_PERSONALITY:
-	case IORING_REGISTER_FILES2:
-	case IORING_REGISTER_FILES_UPDATE2:
-	case IORING_REGISTER_BUFFERS2:
-	case IORING_REGISTER_BUFFERS_UPDATE:
-	case IORING_REGISTER_IOWQ_AFF:
-	case IORING_UNREGISTER_IOWQ_AFF:
-	case IORING_REGISTER_IOWQ_MAX_WORKERS:
-		return false;
-	default:
-		return true;
-	}
-}
-
-static __cold int io_ctx_quiesce(struct io_ring_ctx *ctx)
-{
-	long ret;
-
-	percpu_ref_kill(&ctx->refs);
-
-	/*
-	 * Drop uring mutex before waiting for references to exit. If another
-	 * thread is currently inside io_uring_enter() it might need to grab the
-	 * uring_lock to make progress. If we hold it here across the drain
-	 * wait, then we can deadlock. It's safe to drop the mutex here, since
-	 * no new references will come in after we've killed the percpu ref.
-	 */
-	mutex_unlock(&ctx->uring_lock);
-	do {
-		ret = wait_for_completion_interruptible_timeout(&ctx->ref_comp, HZ);
-		if (ret) {
-			ret = min(0L, ret);
-			break;
-		}
-
-		ret = io_run_task_work_sig();
-		io_req_caches_free(ctx);
-	} while (ret >= 0);
-	mutex_lock(&ctx->uring_lock);
-
-	if (ret)
-		io_refs_resurrect(&ctx->refs, &ctx->ref_comp);
-	return ret;
-}
-
 static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			       void __user *arg, unsigned nr_args)
 	__releases(ctx->uring_lock)
@@ -11103,12 +11045,6 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			return -EACCES;
 	}
 
-	if (io_register_op_must_quiesce(opcode)) {
-		ret = io_ctx_quiesce(ctx);
-		if (ret)
-			return ret;
-	}
-
 	switch (opcode) {
 	case IORING_REGISTER_BUFFERS:
 		ret = io_sqe_buffers_register(ctx, arg, nr_args, NULL);
@@ -11213,11 +11149,6 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 		break;
 	}
 
-	if (io_register_op_must_quiesce(opcode)) {
-		/* bring the ctx back to life */
-		percpu_ref_reinit(&ctx->refs);
-		reinit_completion(&ctx->ref_comp);
-	}
 	return ret;
 }
 
-- 
2.25.1