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From: Dylan Yudaken <[email protected]>
To: <[email protected]>
Cc: <[email protected]>, <[email protected]>,
	Dylan Yudaken <[email protected]>
Subject: [PATCH] io_uring: fix bug in slow unregistering of nodes
Date: Fri, 21 Jan 2022 04:38:56 -0800	[thread overview]
Message-ID: <[email protected]> (raw)

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


             reply	other threads:[~2022-01-21 12:39 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-21 12:38 Dylan Yudaken [this message]
2022-01-21 20:23 ` [PATCH] io_uring: fix bug in slow unregistering of nodes Jens Axboe
2022-01-23 16:36 ` Jens Axboe

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