linux-kernel - [PATCH 5.10 507/717] io_uring: cancel reqs shouldnt kill overflow list

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Date:   Mon, 28 Dec 2020 13:48:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pavel Begunkov <asml.silence@...il.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 507/717] io_uring: cancel reqs shouldnt kill overflow list

From: Pavel Begunkov <asml.silence@...il.com>

[ Upstream commit cda286f0715c82f8117e166afd42cca068876dde ]

io_uring_cancel_task_requests() doesn't imply that the ring is going
away, it may continue to work well after that. The problem is that it
sets ->cq_overflow_flushed effectively disabling the CQ overflow feature

Split setting cq_overflow_flushed from flush, and do the first one only
on exit. It's ok in terms of cancellations because there is a
io_uring->in_idle check in __io_cqring_fill_event().

It also fixes a race with setting ->cq_overflow_flushed in
io_uring_cancel_task_requests, whuch's is not atomic and a part of a
bitmask with other flags. Though, the only other flag that's not set
during init is drain_next, so it's not as bad for sane architectures.

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
Fixes: 0f2122045b946 ("io_uring: don't rely on weak ->files references")
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/io_uring.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index b9d3209a5f9de..e9219841923cc 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1641,10 +1641,6 @@ static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force,
 
 	spin_lock_irqsave(&ctx->completion_lock, flags);
 
-	/* if force is set, the ring is going away. always drop after that */
-	if (force)
-		ctx->cq_overflow_flushed = 1;
-
 	cqe = NULL;
 	list_for_each_entry_safe(req, tmp, &ctx->cq_overflow_list, compl.list) {
 		if (tsk && req->task != tsk)
@@ -8378,6 +8374,8 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 {
 	mutex_lock(&ctx->uring_lock);
 	percpu_ref_kill(&ctx->refs);
+	/* if force is set, the ring is going away. always drop after that */
+	ctx->cq_overflow_flushed = 1;
 	if (ctx->rings)
 		io_cqring_overflow_flush(ctx, true, NULL, NULL);
 	mutex_unlock(&ctx->uring_lock);
-- 
2.27.0