linux-kernel - Re: [PATCH] fs: Fix jfs_fsync() Sleeping in Invalid Context

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Message-ID: <Z-Ly4WmAaN7aev3R@casper.infradead.org>
Date: Tue, 25 Mar 2025 18:16:01 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Purva Yeshi <purvayeshi550@...il.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzbot+219127d0a3bce650e1b6@...kaller.appspotmail.com
Subject: Re: [PATCH] fs: Fix jfs_fsync() Sleeping in Invalid Context

On Tue, Mar 25, 2025 at 11:03:36PM +0530, Purva Yeshi wrote:
> +++ b/fs/direct-io.c
> @@ -356,13 +356,9 @@ static void dio_bio_end_aio(struct bio *bio)
>  			defer_completion = dio->defer_completion ||
>  					   (dio_op == REQ_OP_WRITE &&
>  					    dio->inode->i_mapping->nrpages);
> -		if (defer_completion) {
> -			INIT_WORK(&dio->complete_work, dio_aio_complete_work);
> -			queue_work(dio->inode->i_sb->s_dio_done_wq,
> -				   &dio->complete_work);
> -		} else {
> -			dio_complete(dio, 0, DIO_COMPLETE_ASYNC);
> -		}
> +
> +		INIT_WORK(&dio->complete_work, dio_aio_complete_work);
> +		queue_work(dio->inode->i_sb->s_dio_done_wq, &dio->complete_work);

This patch is definitely wrong.  If it were the right thing to do, then
since defer_completion is now un-read, we should stop calculating it.

I'm not sure what the right solution is; should we simply do:

                        defer_completion = dio->defer_completion ||
+					   in_atomic() ||
                                           (dio_op == REQ_OP_WRITE &&
                                            dio->inode->i_mapping->nrpages);

I'm kind of surprised this problem hasn't cropped up before now ...