linux-kernel - Re: [PATCH Next] iomap: Add sanity check for dio done workqueue

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Message-ID: <aSQi0e8SmY5OVLcS@infradead.org>
Date: Mon, 24 Nov 2025 01:18:09 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Edward Adam Davis <eadavis@...com>
Cc: syzbot+a2b9a4ed0d61b1efb3f5@...kaller.appspotmail.com,
	brauner@...nel.org, djwong@...nel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-xfs@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH Next] iomap: Add sanity check for dio done workqueue

On Mon, Nov 24, 2025 at 04:53:04PM +0800, Edward Adam Davis wrote:
> The s_dio_done_wq was not allocated memory, leading to the null-ptr-deref
> reported by syzbot in [1].
> 
> As shown in [1], we are currently in a soft interrupt context, and we cannot
> use sb_init_dio_done_wq() to allocate memory for wq because it requires a
> mutex lock.
> 
> Added a check to the workqueue; if it is empty, it switches to using a
> synchronous method to end the dio.

Err no.  That sanity check doesn't do anything useful.  Whatever caused
it to be not allocated and allow I/O needs to be fixed.  And I suspect
it's my fault and I already have an idea how to fix, so don't rush it.