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Date: Thu, 15 Aug 2024 07:42:11 +0200
From: Christoph Hellwig <hch@lst.de>
To: John Garry <john.g.garry@oracle.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
	Keith Busch <kbusch@kernel.org>, linux-xfs@vger.kernel.org,
	linux-scsi@vger.kernel.org, linux-block@vger.kernel.org,
	linux-raid@vger.kernel.org, hch@lst.de, axboe@kernel.dk
Subject: Re: [bug report] raid0 array mkfs.xfs hang
Message-ID: <20240815054211.GA12998@lst.de>
References: <8292cfd7-eb9c-4ca7-8eec-321b3738857b@oracle.com> <4d31268f-310b-4220-88a2-e191c3932a82@oracle.com> <ea82050f-f5a4-457d-8603-2f279237c8be@oracle.com> <ZrzDP5c7bRyh7UnE@kbusch-mbp> <yq1wmkjtb1t.fsf@ca-mkp.ca.oracle.com> <441fb8d7-422d-440c-9e12-ab58a0401cad@oracle.com>
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On Wed, Aug 14, 2024 at 06:25:39PM +0100, John Garry wrote:
> On 14/08/2024 15:52, Martin K. Petersen wrote:
>>
>> Keith,
>>
>>> Your change looks fine, though it sounds odd that md raid is changing
>>> queue_limit values outside the limits_lock. The stacking limits should
>>> have set the md device to 0 if one of the member drives doesn't
>>> support write_zeroes, right?
>>
>
> And even if we had used the limits lock to synchronize the update, that 
> only synchronizes writers but not readers (of the limits).

Readers are blocked by freezing the queues (for most drivers) or
doing the internal mddev suspend for md.

So I suspect kicking off a workqueue to do the limits update will
be the right thing going ahead.  For now we'll just need to hack
around by doing single reads of the field.