io_uring: make ctx->timeout_lock a raw spinlock

Chase reports that their tester complaints about a locking context
mismatch:

=============================
[ BUG: Invalid wait context ]
6.13.0-rc1-gf137f14b7ccb-dirty torvalds#9 Not tainted
-----------------------------
syz.1.25198/182604 is trying to lock:
ffff88805e66a358 (&ctx->timeout_lock){-.-.}-{3:3}, at: spin_lock_irq
include/linux/spinlock.h:376 [inline]
ffff88805e66a358 (&ctx->timeout_lock){-.-.}-{3:3}, at:
io_match_task_safe io_uring/io_uring.c:218 [inline]
ffff88805e66a358 (&ctx->timeout_lock){-.-.}-{3:3}, at:
io_match_task_safe+0x187/0x250 io_uring/io_uring.c:204
other info that might help us debug this:
context-{5:5}
1 lock held by syz.1.25198/182604:
 #0: ffff88802b7d48c0 (&acct->lock){+.+.}-{2:2}, at:
io_acct_cancel_pending_work+0x2d/0x6b0 io_uring/io-wq.c:1049
stack backtrace:
CPU: 0 UID: 0 PID: 182604 Comm: syz.1.25198 Not tainted
6.13.0-rc1-gf137f14b7ccb-dirty torvalds#9
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x82/0xd0 lib/dump_stack.c:120
 print_lock_invalid_wait_context kernel/locking/lockdep.c:4826 [inline]
 check_wait_context kernel/locking/lockdep.c:4898 [inline]
 __lock_acquire+0x883/0x3c80 kernel/locking/lockdep.c:5176
 lock_acquire.part.0+0x11b/0x370 kernel/locking/lockdep.c:5849
 __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
 _raw_spin_lock_irq+0x36/0x50 kernel/locking/spinlock.c:170
 spin_lock_irq include/linux/spinlock.h:376 [inline]
 io_match_task_safe io_uring/io_uring.c:218 [inline]
 io_match_task_safe+0x187/0x250 io_uring/io_uring.c:204
 io_acct_cancel_pending_work+0xb8/0x6b0 io_uring/io-wq.c:1052
 io_wq_cancel_pending_work io_uring/io-wq.c:1074 [inline]
 io_wq_cancel_cb+0xb0/0x390 io_uring/io-wq.c:1112
 io_uring_try_cancel_requests+0x15e/0xd70 io_uring/io_uring.c:3062
 io_uring_cancel_generic+0x6ec/0x8c0 io_uring/io_uring.c:3140
 io_uring_files_cancel include/linux/io_uring.h:20 [inline]
 do_exit+0x494/0x27a0 kernel/exit.c:894
 do_group_exit+0xb3/0x250 kernel/exit.c:1087
 get_signal+0x1d77/0x1ef0 kernel/signal.c:3017
 arch_do_signal_or_restart+0x79/0x5b0 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x150/0x2a0 kernel/entry/common.c:218
 do_syscall_64+0xd8/0x250 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

which is because io_uring has ctx->timeout_lock nesting inside the
io-wq acct lock, the latter of which is used from inside the scheduler
and hence is a raw spinlock, while the former is a "normal" spinlock
and can hence be sleeping on PREEMPT_RT.

Change ctx->timeout_lock to be a raw spinlock to solve this nesting
dependency on PREEMPT_RT=y.

Reported-by: chase xd <sl1589472800@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

include/linux/io_uring_types.h

@@ -345,7 +345,7 @@ struct io_ring_ctx {
 
 	/* timeouts */
 	struct {
-		spinlock_t		timeout_lock;
+		raw_spinlock_t		timeout_lock;
 		struct list_head	timeout_list;
 		struct list_head	ltimeout_list;
 		unsigned		cq_last_tm_flush;

io_uring/io_uring.c

@@ -215,9 +215,9 @@ bool io_match_task_safe(struct io_kiocb *head, struct io_uring_task *tctx,
 		struct io_ring_ctx *ctx = head->ctx;
 
 		/* protect against races with linked timeouts */
-		spin_lock_irq(&ctx->timeout_lock);
+		raw_spin_lock_irq(&ctx->timeout_lock);
 		matched = io_match_linked(head);
-		spin_unlock_irq(&ctx->timeout_lock);
+		raw_spin_unlock_irq(&ctx->timeout_lock);
 	} else {
 		matched = io_match_linked(head);
 	}
@@ -333,7 +333,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	init_waitqueue_head(&ctx->cq_wait);
 	init_waitqueue_head(&ctx->poll_wq);
 	spin_lock_init(&ctx->completion_lock);
-	spin_lock_init(&ctx->timeout_lock);
+	raw_spin_lock_init(&ctx->timeout_lock);
 	INIT_WQ_LIST(&ctx->iopoll_list);
 	INIT_LIST_HEAD(&ctx->io_buffers_comp);
 	INIT_LIST_HEAD(&ctx->defer_list);
@@ -498,10 +498,10 @@ static void io_prep_async_link(struct io_kiocb *req)
 	if (req->flags & REQ_F_LINK_TIMEOUT) {
 		struct io_ring_ctx *ctx = req->ctx;
 
-		spin_lock_irq(&ctx->timeout_lock);
+		raw_spin_lock_irq(&ctx->timeout_lock);
 		io_for_each_link(cur, req)
 			io_prep_async_work(cur);
-		spin_unlock_irq(&ctx->timeout_lock);
+		raw_spin_unlock_irq(&ctx->timeout_lock);
 	} else {
 		io_for_each_link(cur, req)
 			io_prep_async_work(cur);

io_uring/timeout.c

@@ -74,10 +74,10 @@ static void io_timeout_complete(struct io_kiocb *req, struct io_tw_state *ts)
 	if (!io_timeout_finish(timeout, data)) {
 		if (io_req_post_cqe(req, -ETIME, IORING_CQE_F_MORE)) {
 			/* re-arm timer */
-			spin_lock_irq(&ctx->timeout_lock);
+			raw_spin_lock_irq(&ctx->timeout_lock);
 			list_add(&timeout->list, ctx->timeout_list.prev);
 			hrtimer_start(&data->timer, timespec64_to_ktime(data->ts), data->mode);
-			spin_unlock_irq(&ctx->timeout_lock);
+			raw_spin_unlock_irq(&ctx->timeout_lock);
 			return;
 		}
 	}
@@ -109,7 +109,7 @@ __cold void io_flush_timeouts(struct io_ring_ctx *ctx)
 	u32 seq;
 	struct io_timeout *timeout, *tmp;
 
-	spin_lock_irq(&ctx->timeout_lock);
+	raw_spin_lock_irq(&ctx->timeout_lock);
 	seq = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts);
 
 	list_for_each_entry_safe(timeout, tmp, &ctx->timeout_list, list) {
@@ -134,7 +134,7 @@ __cold void io_flush_timeouts(struct io_ring_ctx *ctx)
 		io_kill_timeout(req, 0);
 	}
 	ctx->cq_last_tm_flush = seq;
-	spin_unlock_irq(&ctx->timeout_lock);
+	raw_spin_unlock_irq(&ctx->timeout_lock);
 }
 
 static void io_req_tw_fail_links(struct io_kiocb *link, struct io_tw_state *ts)
@@ -200,9 +200,9 @@ void io_disarm_next(struct io_kiocb *req)
 	} else if (req->flags & REQ_F_LINK_TIMEOUT) {
 		struct io_ring_ctx *ctx = req->ctx;
 
-		spin_lock_irq(&ctx->timeout_lock);
+		raw_spin_lock_irq(&ctx->timeout_lock);
 		link = io_disarm_linked_timeout(req);
-		spin_unlock_irq(&ctx->timeout_lock);
+		raw_spin_unlock_irq(&ctx->timeout_lock);
 		if (link)
 			io_req_queue_tw_complete(link, -ECANCELED);
 	}
@@ -238,11 +238,11 @@ static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer)
 	struct io_ring_ctx *ctx = req->ctx;
 	unsigned long flags;
 
-	spin_lock_irqsave(&ctx->timeout_lock, flags);
+	raw_spin_lock_irqsave(&ctx->timeout_lock, flags);
 	list_del_init(&timeout->list);
 	atomic_set(&req->ctx->cq_timeouts,
 		atomic_read(&req->ctx->cq_timeouts) + 1);
-	spin_unlock_irqrestore(&ctx->timeout_lock, flags);
+	raw_spin_unlock_irqrestore(&ctx->timeout_lock, flags);
 
 	if (!(data->flags & IORING_TIMEOUT_ETIME_SUCCESS))
 		req_set_fail(req);
@@ -285,9 +285,9 @@ int io_timeout_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd)
 {
 	struct io_kiocb *req;
 
-	spin_lock_irq(&ctx->timeout_lock);
+	raw_spin_lock_irq(&ctx->timeout_lock);
 	req = io_timeout_extract(ctx, cd);
-	spin_unlock_irq(&ctx->timeout_lock);
+	raw_spin_unlock_irq(&ctx->timeout_lock);
 
 	if (IS_ERR(req))
 		return PTR_ERR(req);
@@ -330,7 +330,7 @@ static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer)
 	struct io_ring_ctx *ctx = req->ctx;
 	unsigned long flags;
 
-	spin_lock_irqsave(&ctx->timeout_lock, flags);
+	raw_spin_lock_irqsave(&ctx->timeout_lock, flags);
 	prev = timeout->head;
 	timeout->head = NULL;
 
@@ -345,7 +345,7 @@ static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer)
 	}
 	list_del(&timeout->list);
 	timeout->prev = prev;
-	spin_unlock_irqrestore(&ctx->timeout_lock, flags);
+	raw_spin_unlock_irqrestore(&ctx->timeout_lock, flags);
 
 	req->io_task_work.func = io_req_task_link_timeout;
 	io_req_task_work_add(req);
@@ -472,12 +472,12 @@ int io_timeout_remove(struct io_kiocb *req, unsigned int issue_flags)
 	} else {
 		enum hrtimer_mode mode = io_translate_timeout_mode(tr->flags);
 
-		spin_lock_irq(&ctx->timeout_lock);
+		raw_spin_lock_irq(&ctx->timeout_lock);
 		if (tr->ltimeout)
 			ret = io_linked_timeout_update(ctx, tr->addr, &tr->ts, mode);
 		else
 			ret = io_timeout_update(ctx, tr->addr, &tr->ts, mode);
-		spin_unlock_irq(&ctx->timeout_lock);
+		raw_spin_unlock_irq(&ctx->timeout_lock);
 	}
 
 	if (ret < 0)
@@ -572,7 +572,7 @@ int io_timeout(struct io_kiocb *req, unsigned int issue_flags)
 	struct list_head *entry;
 	u32 tail, off = timeout->off;
 
-	spin_lock_irq(&ctx->timeout_lock);
+	raw_spin_lock_irq(&ctx->timeout_lock);
 
 	/*
 	 * sqe->off holds how many events that need to occur for this
@@ -611,7 +611,7 @@ int io_timeout(struct io_kiocb *req, unsigned int issue_flags)
 	list_add(&timeout->list, entry);
 	data->timer.function = io_timeout_fn;
 	hrtimer_start(&data->timer, timespec64_to_ktime(data->ts), data->mode);
-	spin_unlock_irq(&ctx->timeout_lock);
+	raw_spin_unlock_irq(&ctx->timeout_lock);
 	return IOU_ISSUE_SKIP_COMPLETE;
 }
 
@@ -620,7 +620,7 @@ void io_queue_linked_timeout(struct io_kiocb *req)
 	struct io_timeout *timeout = io_kiocb_to_cmd(req, struct io_timeout);
 	struct io_ring_ctx *ctx = req->ctx;
 
-	spin_lock_irq(&ctx->timeout_lock);
+	raw_spin_lock_irq(&ctx->timeout_lock);
 	/*
 	 * If the back reference is NULL, then our linked request finished
 	 * before we got a chance to setup the timer
@@ -633,7 +633,7 @@ void io_queue_linked_timeout(struct io_kiocb *req)
 				data->mode);
 		list_add_tail(&timeout->list, &ctx->ltimeout_list);
 	}
-	spin_unlock_irq(&ctx->timeout_lock);
+	raw_spin_unlock_irq(&ctx->timeout_lock);
 	/* drop submission reference */
 	io_put_req(req);
 }
@@ -668,15 +668,15 @@ __cold bool io_kill_timeouts(struct io_ring_ctx *ctx, struct io_uring_task *tctx
 	 * timeout_lockfirst to keep locking ordering.
 	 */
 	spin_lock(&ctx->completion_lock);
-	spin_lock_irq(&ctx->timeout_lock);
+	raw_spin_lock_irq(&ctx->timeout_lock);
 	list_for_each_entry_safe(timeout, tmp, &ctx->timeout_list, list) {
 		struct io_kiocb *req = cmd_to_io_kiocb(timeout);
 
 		if (io_match_task(req, tctx, cancel_all) &&
 		    io_kill_timeout(req, -ECANCELED))
 			canceled++;
 	}
-	spin_unlock_irq(&ctx->timeout_lock);
+	raw_spin_unlock_irq(&ctx->timeout_lock);
 	spin_unlock(&ctx->completion_lock);
 	return canceled != 0;
 }