linux-kernel - Re: block: Don't invalidate pagecache for invalid falloc modes

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Message-ID: <ZScKlejOlxIXYmWI@redhat.com>
Date:   Wed, 11 Oct 2023 16:50:29 -0400
From:   Mike Snitzer <snitzer@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Sarthak Kukreti <sarthakkukreti@...omium.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bart Van Assche <bvanassche@....org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        stable@...r.kernel.org, "Darrick J . Wong" <djwong@...nel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: block: Don't invalidate pagecache for invalid falloc modes

On Wed, Oct 11 2023 at  4:20P -0400,
Jens Axboe <axboe@...nel.dk> wrote:

> On 10/11/23 2:12 PM, Sarthak Kukreti wrote:
> > Only call truncate_bdev_range() if the fallocate mode is
> > supported. This fixes a bug where data in the pagecache
> > could be invalidated if the fallocate() was called on the
> > block device with an invalid mode.
> 
> Fix looks fine, but would be nicer if we didn't have to duplicate the
> truncate_bdev_range() in each switch clause. Can we check this upfront
> instead?

No, if you look at the function (rather than just the patch in
isolation) we need to make the call for each case rather than collapse
to a single call at the front (that's the reason for this fix, because
otherwise the default: error case will invalidate the page cache too).

Just so you're aware, I also had this feedback that shaped the patch a
bit back in April:
https://listman.redhat.com/archives/dm-devel/2023-April/053986.html

> Also, please wrap commit messages at 72-74 chars.

Not seeing where the header should be wrapped.  You referring to the
Fixes: line?  I've never seen those wrapped.

Mike