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io_uring: cancel reqs shouldn't kill overflow list

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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@gmail.com>
Fixes: 0f2122045b ("io_uring: don't rely on weak ->files references")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2020-12-17 00:24:35 +00:00 committed by Jens Axboe
parent 4bc4a91253
commit cda286f071
1 changed files with 2 additions and 4 deletions
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6
fs/io_uring.c
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@ -1733,10 +1733,6 @@ 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 (!io_match_task(req, tsk, files))
@ -8655,6 +8651,8 @@ 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);