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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.11 09/31] io_uring: dont keep looping for more events if we cant flush overflow
Date:   Fri, 19 Mar 2021 13:19:03 +0100
Message-Id: <20210319121747.504718297@linuxfoundation.org>
In-Reply-To: <20210319121747.203523570@linuxfoundation.org>
References: <20210319121747.203523570@linuxfoundation.org>
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From: Jens Axboe <axboe@kernel.dk>

[ Upstream commit ca0a26511c679a797f86589894a4523db36d833e ]

It doesn't make sense to wait for more events to come in, if we can't
even flush the overflow we already have to the ring. Return -EBUSY for
that condition, just like we do for attempts to submit with overflow
pending.

Cc: stable@vger.kernel.org # 5.11
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/io_uring.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7621978e9fc8..cab380a337e4 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1823,18 +1823,22 @@ static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force,
 	return all_flushed;
 }
 
-static void io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force,
+static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force,
 				     struct task_struct *tsk,
 				     struct files_struct *files)
 {
+	bool ret = true;
+
 	if (test_bit(0, &ctx->cq_check_overflow)) {
 		/* iopoll syncs against uring_lock, not completion_lock */
 		if (ctx->flags & IORING_SETUP_IOPOLL)
 			mutex_lock(&ctx->uring_lock);
-		__io_cqring_overflow_flush(ctx, force, tsk, files);
+		ret = __io_cqring_overflow_flush(ctx, force, tsk, files);
 		if (ctx->flags & IORING_SETUP_IOPOLL)
 			mutex_unlock(&ctx->uring_lock);
 	}
+
+	return ret;
 }
 
 static void __io_cqring_fill_event(struct io_kiocb *req, long res, long cflags)
@@ -7280,11 +7284,16 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 	iowq.nr_timeouts = atomic_read(&ctx->cq_timeouts);
 	trace_io_uring_cqring_wait(ctx, min_events);
 	do {
-		io_cqring_overflow_flush(ctx, false, NULL, NULL);
+		/* if we can't even flush overflow, don't wait for more */
+		if (!io_cqring_overflow_flush(ctx, false, NULL, NULL)) {
+			ret = -EBUSY;
+			break;
+		}
 		prepare_to_wait_exclusive(&ctx->wait, &iowq.wq,
 						TASK_INTERRUPTIBLE);
 		ret = io_cqring_wait_schedule(ctx, &iowq, &timeout);
 		finish_wait(&ctx->wait, &iowq.wq);
+		cond_resched();
 	} while (ret > 0);
 
 	restore_saved_sigmask_unless(ret == -EINTR);
-- 
2.30.1