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io_uring: fix bug in slow unregistering of nodes 

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.

Fixes: 4a38aed2a0 ("io_uring: batch reap of dead file registrations")
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220121123856.3557884-1-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Dylan Yudaken 2022-01-21 04:38:56 -08:00 committed by Jens Axboe
parent dd81e1c7d5
commit b36a205004
1 changed files with 6 additions and 1 deletions
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7
fs/io_uring.c
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@ -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)