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From: Daniel Wagner <dwagner@suse.de>
To: Christoph Hellwig <hch@lst.de>
Cc: Chris Leech <cleech@redhat.com>,
	linux-nvme@lists.infradead.org, sagi@grimberg.me,
	lengchao@huawei.com, hare@suse.de, mlombard@redhat.com,
	jmeneghi@redhat.com
Subject: Re: [RFC PATCH] nvme-multipath: break endless loop in nvme_round_robin_path
Date: Tue, 22 Mar 2022 13:07:27 +0100	[thread overview]
Message-ID: <20220322120727.k2drakwc4sr4rclq@carbon.lan> (raw)
In-Reply-To: <20220322111743.GC29151@lst.de>

On Tue, Mar 22, 2022 at 12:17:43PM +0100, Christoph Hellwig wrote:
> On Mon, Mar 21, 2022 at 03:43:03PM -0700, Chris Leech wrote:
> > This is a backstop for the odd loop construct in nvme_round_robin_path.
> > It counts how many times the head pointer has been passed, as that's the
> > only thing guarenteed to stay on the list.  Once is needed to start from
> > a different place and check the entire list, twice is excessive looping.
> 
> Shouldn't

d1bcf006a9d3 ("nvme-multipath: Early exit if no path is available")

> take care of this?

IIRC, this addressed the issue that we started to dereference a NULL
pointer if there was no path left.

Chris' problem is that the iterator always returns the same
pointer. Personally, I prefer the solution to introduce some sort of
sentinel over the one with the locking.


  reply	other threads:[~2022-03-22 12:07 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-21 22:43 nvme-multipath: round-robin infinite looping Chris Leech
2022-03-21 22:43 ` kdump details (Re: nvme-multipath: round-robin infinite looping) Chris Leech
2022-03-22 11:16   ` Christoph Hellwig
2022-03-22 15:36     ` Chris Leech
2022-03-21 22:43 ` [RFC PATCH] nvme-multipath: break endless loop in nvme_round_robin_path Chris Leech
2022-03-22 11:17   ` Christoph Hellwig
2022-03-22 12:07     ` Daniel Wagner [this message]
2022-03-22 15:42     ` Chris Leech
2022-03-21 22:43 ` [RFC PATCH] nvme: fix RCU hole that allowed for endless looping in multipath round robin Chris Leech
2022-03-23 14:54   ` Sagi Grimberg
2022-03-23 15:34     ` Christoph Hellwig
2022-03-23 19:07       ` John Meneghini
2022-04-05 13:14         ` John Meneghini
2022-03-25  6:36   ` Christoph Hellwig
2022-03-25 12:42   ` Sagi Grimberg
2022-04-05 17:25     ` Chris Leech

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