linux-kernel - Re: [PATCH] drbd: do not set REQ_PREFLUSH when submitting barrier

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Message-ID: <ZFHgefWofVt24tRl@infradead.org>
Date:   Tue, 2 May 2023 21:18:01 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Christoph Böhmwalder 
        <christoph.boehmwalder@...bit.com>
Cc:     Jens Axboe <axboe@...nel.dk>, drbd-dev@...ts.linbit.com,
        linux-kernel@...r.kernel.org,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        linux-block@...r.kernel.org, Thomas Voegtle <tv@...96.de>
Subject: Re: [PATCH] drbd: do not set REQ_PREFLUSH when submitting barrier

On Tue, May 02, 2023 at 11:29:22AM +0200, Christoph Böhmwalder wrote:
>  	struct bio *bio = bio_alloc(device->ldev->backing_bdev, 0,
> -				    REQ_OP_FLUSH | REQ_PREFLUSH, GFP_NOIO);
> +				    REQ_OP_FLUSH, GFP_NOIO);

This isn't going to work.  flush bios are (somewhat confusingly)
implemented as writes with no data and the preflush flag.  So this
should be:

	REQ_OP_WRITE | REQ_PREFLUSH.

and it looks like whatever flushing this does hasn't wroked for a long
time.