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Date: Tue, 25 Nov 2025 03:10:09 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Gao Xiang <hsiangkao@linux.alibaba.com>
Cc: Ming Lei <ming.lei@redhat.com>, Christoph Hellwig <hch@infradead.org>,
	linux-block@vger.kernel.org, Mikulas Patocka <mpatocka@redhat.com>,
	Zhaoyang Huang <zhaoyang.huang@unisoc.com>,
	Dave Chinner <dchinner@redhat.com>, linux-fsdevel@vger.kernel.org,
	Jens Axboe <axboe@kernel.dk>
Subject: Re: calling into file systems directly from ->queue_rq, was Re:
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On Tue, Nov 25, 2025 at 06:57:15PM +0800, Gao Xiang wrote:
> I've said there is no clear list of which data needs to be
> saved/restored.
> 
> FSes can do _anything_. Maybe something in `current` needs
> to be saved, but anything that uses `current`/PID as
> a mapping key also needs to be saved, e.g., arbitrary
> 
> `hash_table[current]` or `context_table[current->pid]`.
> 
> Again, because not all filesystems allow nesting by design:
> Linux kernel doesn't need block filesystem to be nested.

Yes.  Various other PF_ flags also come to mind.  Or Kent's
magic fault disabling flag (although with bcachefs gone we can
probably remove that, thinking of it).