* [PATCH] io_uring: fix bug in slow unregistering of nodes
@ 2022-01-21 12:38 Dylan Yudaken
2022-01-21 20:23 ` Jens Axboe
2022-01-23 16:36 ` Jens Axboe
0 siblings, 2 replies; 3+ messages in thread
From: Dylan Yudaken @ 2022-01-21 12:38 UTC (permalink / raw)
To: io-uring; +Cc: axboe, asml.silence, Dylan Yudaken
In some cases io_rsrc_ref_quiesce will call io_rsrc_node_switch_start,
and then immediately flush the delayed work queue &ctx->rsrc_put_work.
However the percpu_ref_put does not immediately destroy the node, it
will be called asynchronously via RCU. That ends up with
io_rsrc_node_ref_zero only being called after rsrc_put_work has been
flushed, and so the process ends up sleeping for 1 second unnecessarily.
This patch executes the put code immediately if we are busy
quiescing.
Signed-off-by: Dylan Yudaken <[email protected]>
---
fs/io_uring.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index e54c4127422e..dd4c801c7afd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7822,10 +7822,15 @@ static __cold void io_rsrc_node_ref_zero(struct percpu_ref *ref)
struct io_ring_ctx *ctx = node->rsrc_data->ctx;
unsigned long flags;
bool first_add = false;
+ unsigned long delay = HZ;
spin_lock_irqsave(&ctx->rsrc_ref_lock, flags);
node->done = true;
+ /* if we are mid-quiesce then do not delay */
+ if (node->rsrc_data->quiesce)
+ delay = 0;
+
while (!list_empty(&ctx->rsrc_ref_list)) {
node = list_first_entry(&ctx->rsrc_ref_list,
struct io_rsrc_node, node);
@@ -7838,7 +7843,7 @@ static __cold void io_rsrc_node_ref_zero(struct percpu_ref *ref)
spin_unlock_irqrestore(&ctx->rsrc_ref_lock, flags);
if (first_add)
- mod_delayed_work(system_wq, &ctx->rsrc_put_work, HZ);
+ mod_delayed_work(system_wq, &ctx->rsrc_put_work, delay);
}
static struct io_rsrc_node *io_rsrc_node_alloc(struct io_ring_ctx *ctx)
--
2.30.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] io_uring: fix bug in slow unregistering of nodes
2022-01-21 12:38 [PATCH] io_uring: fix bug in slow unregistering of nodes Dylan Yudaken
@ 2022-01-21 20:23 ` Jens Axboe
2022-01-23 16:36 ` Jens Axboe
1 sibling, 0 replies; 3+ messages in thread
From: Jens Axboe @ 2022-01-21 20:23 UTC (permalink / raw)
To: Dylan Yudaken, io-uring; +Cc: asml.silence
On 1/21/22 5:38 AM, Dylan Yudaken wrote:
> In some cases io_rsrc_ref_quiesce will call io_rsrc_node_switch_start,
> and then immediately flush the delayed work queue &ctx->rsrc_put_work.
>
> However the percpu_ref_put does not immediately destroy the node, it
> will be called asynchronously via RCU. That ends up with
> io_rsrc_node_ref_zero only being called after rsrc_put_work has been
> flushed, and so the process ends up sleeping for 1 second unnecessarily.
>
> This patch executes the put code immediately if we are busy
> quiescing.
Looks good to me, and as far as I can tell, this bug was introduced by:
commit 4a38aed2a0a729ccecd84dca5b76d827b9e1294d
Author: Jens Axboe <[email protected]>
Date: Thu May 14 17:21:15 2020 -0600
io_uring: batch reap of dead file registrations
so I'll add a fixes line to that effect to the commit. Thanks!
--
Jens Axboe
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] io_uring: fix bug in slow unregistering of nodes
2022-01-21 12:38 [PATCH] io_uring: fix bug in slow unregistering of nodes Dylan Yudaken
2022-01-21 20:23 ` Jens Axboe
@ 2022-01-23 16:36 ` Jens Axboe
1 sibling, 0 replies; 3+ messages in thread
From: Jens Axboe @ 2022-01-23 16:36 UTC (permalink / raw)
To: Dylan Yudaken, io-uring; +Cc: asml.silence
On Fri, 21 Jan 2022 04:38:56 -0800, Dylan Yudaken wrote:
> In some cases io_rsrc_ref_quiesce will call io_rsrc_node_switch_start,
> and then immediately flush the delayed work queue &ctx->rsrc_put_work.
>
> However the percpu_ref_put does not immediately destroy the node, it
> will be called asynchronously via RCU. That ends up with
> io_rsrc_node_ref_zero only being called after rsrc_put_work has been
> flushed, and so the process ends up sleeping for 1 second unnecessarily.
>
> [...]
Applied, thanks!
[1/1] io_uring: fix bug in slow unregistering of nodes
(no commit info)
Best regards,
--
Jens Axboe
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-01-21 12:38 [PATCH] io_uring: fix bug in slow unregistering of nodes Dylan Yudaken
2022-01-21 20:23 ` Jens Axboe
2022-01-23 16:36 ` Jens Axboe
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