linux-ext4 - Re: [PATCH -v3] ext4: don't BUG if kernel subsystems dirty pages without asking ext4 first

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Message-ID: <YhmJ2EfZv0TqRX+h@mit.edu>
Date:   Fri, 25 Feb 2022 21:00:56 -0500
From:   "Theodore Ts'o" <tytso@....edu>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        Lee Jones <lee.jones@...aro.org>, linux-ext4@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Dave Chinner <dchinner@...hat.com>,
        Goldwyn Rodrigues <rgoldwyn@...e.com>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Bob Peterson <rpeterso@...hat.com>,
        Damien Le Moal <damien.lemoal@....com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johannes Thumshirn <jth@...nel.org>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, cluster-devel@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -v3] ext4: don't BUG if kernel subsystems dirty pages
 without asking ext4 first

On Fri, Feb 25, 2022 at 08:40:36PM -0500, Theodore Ts'o wrote:
> Well, that makes it process_vm_writev()'s is that it needs to know
> when to call pin_user_file_pages().

Sorry, typed too fast.  What I was trying to say is this make it
process_vm_writev()'s problem to figure out when it should call
pin_user_file_pages() versus some other pin_user_pages function.

> I suspect that for many use cases
> --- for example, if this is being used by a debugger to modify a
> variable on a stack, or an anonymous page in the program's data
> segment, process_vm_writev() *isn't* actually pinning a file.  So they
> want some kind of interface that automatically DTRT regardless of
> whether the user pages being edited are file-backed or not
> file-backed.

					- Ted