linux-kernel - Re: [PATCH] drbd: always set BLK_FEAT_STABLE

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Message-ID: <aYWNhtixUGuj3hat@infradead.org>
Date: Thu, 5 Feb 2026 22:43:18 -0800
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
Subject: Re: [PATCH] drbd: always set BLK_FEAT_STABLE_WRITES

On Thu, Feb 05, 2026 at 06:39:29PM +0100, Christoph Böhmwalder wrote:
> DRBD requires stable pages because it may read the same bio data
> multiple times for local disk I/O and network transmission, and in
> some cases for calculating checksums.
> 
> The BLK_FEAT_STABLE_WRITES flag is set when the device is first
> created, but blk_set_stacking_limits() clears it whenever a
> backing device is attached. In some cases the flag may be
> inherited from the backing device, but we want it to be enabled
> at all times.

This looks like a bug.  If an underlying device requires
BLK_FEAT_STABLE_WRITES, the upper device needs to inherit it.

> Note: this commit is based on the for-6.19/block tree in case it is
> still possible to take it into the 6.19 release as this *could* lead
> to silent data corruption. However, due to other protection
> mechanisms in DRBD, this is relatively unlikely to happen in the
> real world and we have not seen any corresponding reports from users.
> So if this only lands in 6.20/7.0, it is also fine.

I'm fine with this as a hot fix for 6.19 and -stable:

Reviewed-by: Christoph Hellwig <hch@....de>

But can you please also do the proper block layer fix and then
revert the drbd one?