From 41d3a6bd1d37149b18331fc4bb789c5456a7aeb0 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Mon, 13 Sep 2021 13:08:51 -0600
Subject: [PATCH] io_uring: pin SQPOLL data before unlocking ring lock
Git-commit: 41d3a6bd1d37149b18331fc4bb789c5456a7aeb0
Patch-mainline: v5.15-rc2
References: git-fixes

We need to re-check sqd->thread after we've dropped the lock. Pin
the sqd before doing the lockdep lock dance, and check if the thread
is alive after that. It's either NULL or alive, as the SQPOLL thread
cannot exit without holding the same sqd->lock.

Reported-and-tested-by: syzbot+337de45f13a4fd54d708@syzkaller.appspotmail.com
Fixes: fa84693b3c89 ("io_uring: ensure IORING_REGISTER_IOWQ_MAX_WORKERS works with SQPOLL")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
---
 fs/io_uring.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 66a7414c3756..a864a94364c6 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -10563,10 +10563,12 @@ static int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 			 * ordering. Fine to drop uring_lock here, we hold
 			 * a ref to the ctx.
 			 */
+			refcount_inc(&sqd->refs);
 			mutex_unlock(&ctx->uring_lock);
 			mutex_lock(&sqd->lock);
 			mutex_lock(&ctx->uring_lock);
-			tctx = sqd->thread->io_uring;
+			if (sqd->thread)
+				tctx = sqd->thread->io_uring;
 		}
 	} else {
 		tctx = current->io_uring;
@@ -10580,16 +10582,20 @@ static int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 	if (ret)
 		goto err;
 
-	if (sqd)
+	if (sqd) {
 		mutex_unlock(&sqd->lock);
+		io_put_sq_data(sqd);
+	}
 
 	if (copy_to_user(arg, new_count, sizeof(new_count)))
 		return -EFAULT;
 
 	return 0;
 err:
-	if (sqd)
+	if (sqd) {
 		mutex_unlock(&sqd->lock);
+		io_put_sq_data(sqd);
+	}
 	return ret;
 }
 
-- 
2.35.3