From 41d3a6bd1d37149b18331fc4bb789c5456a7aeb0 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Mon, 13 Sep 2021 13:08:51 -0600 Subject: [PATCH] io_uring: pin SQPOLL data before unlocking ring lock 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 --- 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 66a7414..a864a94 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; } -- 2.7.4