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io_uring: don't submit sqes when ctx->refs is dying

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When IORING_SETUP_SQPOLL is enabled, io_ring_ctx_wait_and_kill() will wait
for sq thread to idle by busy loop:

    while (ctx->sqo_thread && !wq_has_sleeper(&ctx->sqo_wait))
        cond_resched();

Above loop isn't very CPU friendly, it may introduce a short cpu burst on
the current cpu.

If ctx->refs is dying, we forbid sq_thread from submitting any further
SQEs. Instead they just get discarded when we exit.

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Xiaoguang Wang 2020-05-20 15:35:03 +08:00 committed by Jens Axboe
parent 310672552f
commit 6b668c9b7f
1 changed files with 2 additions and 11 deletions
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13
fs/io_uring.c
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@ -6175,7 +6175,8 @@ static int io_sq_thread(void *data)
}
mutex_lock(&ctx->uring_lock);
ret = io_submit_sqes(ctx, to_submit, NULL, -1);
if (likely(!percpu_ref_is_dying(&ctx->refs)))
ret = io_submit_sqes(ctx, to_submit, NULL, -1);
mutex_unlock(&ctx->uring_lock);
timeout = jiffies + ctx->sq_thread_idle;
}
@ -7465,16 +7466,6 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
percpu_ref_kill(&ctx->refs);
mutex_unlock(&ctx->uring_lock);
/*
* Wait for sq thread to idle, if we have one. It won't spin on new
* work after we've killed the ctx ref above. This is important to do
* before we cancel existing commands, as the thread could otherwise
* be queueing new work post that. If that's work we need to cancel,
* it could cause shutdown to hang.
*/
while (ctx->sqo_thread && !wq_has_sleeper(&ctx->sqo_wait))
cond_resched();
io_kill_timeouts(ctx);
io_poll_remove_all(ctx);