linux-kernel - [PATCH] io_uring/io-wq: don't clear PF_IO

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Date:   Mon, 12 Jun 2023 12:11:57 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     io-uring <io-uring@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Chinner <david@...morbit.com>,
        Zorro Lang <zlang@...hat.com>
Subject: [PATCH] io_uring/io-wq: don't clear PF_IO_WORKER on exit

A recent commit gated the core dumping task exit logic on current->flags
remaining consistent in terms of PF_{IO,USER}_WORKER at task exit time.
This exposed a problem with the io-wq handling of that, which explicitly
clears PF_IO_WORKER before calling do_exit().

The reasons for this manual clear of PF_IO_WORKER is historical, where
io-wq used to potentially trigger a sleep on exit. As the io-wq thread
is exiting, it should not participate any further accounting. But these
days we don't need to rely on current->flags anymore, so we can safely
remove the PF_IO_WORKER clearing.

Reported-by: Zorro Lang <zlang@...hat.com>
Reported-by: Dave Chinner <david@...morbit.com>
Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Link: https://lore.kernel.org/all/ZIZSPyzReZkGBEFy@dread.disaster.area/
Fixes: f9010dbdce91 ("fork, vhost: Use CLONE_THREAD to fix freezer/ps regression")
Signed-off-by: Jens Axboe <axboe@...nel.dk>

---

diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c
index b2715988791e..fe38eb0cbc82 100644
--- a/io_uring/io-wq.c
+++ b/io_uring/io-wq.c
@@ -221,9 +221,6 @@ static void io_worker_exit(struct io_worker *worker)
 	raw_spin_unlock(&wq->lock);
 	io_wq_dec_running(worker);
 	worker->flags = 0;
-	preempt_disable();
-	current->flags &= ~PF_IO_WORKER;
-	preempt_enable();

 	kfree_rcu(worker, rcu);
 	io_worker_ref_put(wq);

-- 
Jens Axboe