From: "Marek Marczykowski-Górecki" <email@example.com> To: Michael Brown <firstname.lastname@example.org> Cc: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [PATCH] xen-netback: Check for hotplug-status existence before watching Date: Mon, 10 May 2021 20:53:02 +0200 [thread overview] Message-ID: <YJmBDpqQ12ZBGf58@mail-itl> (raw) In-Reply-To: <firstname.lastname@example.org> [-- Attachment #1: Type: text/plain, Size: 2328 bytes --] On Mon, May 10, 2021 at 07:47:01PM +0100, Michael Brown wrote: > On 10/05/2021 19:32, Marek Marczykowski-Górecki wrote: > > On Tue, Apr 13, 2021 at 04:25:12PM +0100, Michael Brown wrote: > > > The logic in connect() is currently written with the assumption that > > > xenbus_watch_pathfmt() will return an error for a node that does not > > > exist. This assumption is incorrect: xenstore does allow a watch to > > > be registered for a nonexistent node (and will send notifications > > > should the node be subsequently created). > > > > > > As of commit 1f2565780 ("xen-netback: remove 'hotplug-status' once it > > > has served its purpose"), this leads to a failure when a domU > > > transitions into XenbusStateConnected more than once. On the first > > > domU transition into Connected state, the "hotplug-status" node will > > > be deleted by the hotplug_status_changed() callback in dom0. On the > > > second or subsequent domU transition into Connected state, the > > > hotplug_status_changed() callback will therefore never be invoked, and > > > so the backend will remain stuck in InitWait. > > > > > > This failure prevents scenarios such as reloading the xen-netfront > > > module within a domU, or booting a domU via iPXE. There is > > > unfortunately no way for the domU to work around this dom0 bug. > > > > > > Fix by explicitly checking for existence of the "hotplug-status" node, > > > thereby creating the behaviour that was previously assumed to exist. > > > > This change is wrong. The 'hotplug-status' node is created _only_ by a > > hotplug script and done so when it's executed. When kernel waits for > > hotplug script to be executed it waits for the node to _appear_, not > > _change_. So, this change basically made the kernel not waiting for the > > hotplug script at all. > > That doesn't sound plausible to me. In the setup as you describe, how is > the kernel expected to differentiate between "hotplug script has not yet > created the node" and "hotplug script does not exist and will therefore > never create any node"? Is the later valid at all? From what I can see in the toolstack, it always sets some hotplug script (if not specified explicitly - then "vif-bridge"), -- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 488 bytes --]
next prev parent reply other threads:[~2021-05-10 18:53 UTC|newest] Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-10 18:25 xen-netback hotplug-status regression bug Michael Brown 2021-04-13 7:12 ` Paul Durrant 2021-04-13 10:48 ` Michael Brown 2021-04-13 10:55 ` Paul Durrant 2021-04-13 15:14 ` Michael Brown 2021-04-13 15:25 ` [PATCH] xen-netback: Check for hotplug-status existence before watching Michael Brown 2021-04-13 19:12 ` Paul Durrant 2021-04-13 22:30 ` patchwork-bot+netdevbpf 2021-05-10 18:32 ` Marek Marczykowski-Górecki 2021-05-10 18:47 ` Michael Brown 2021-05-10 18:53 ` Marek Marczykowski-Górecki [this message] 2021-05-10 19:06 ` Michael Brown 2021-05-10 19:42 ` Marek Marczykowski-Górecki 2021-05-11 7:06 ` Durrant, Paul 2021-05-11 10:40 ` Marek Marczykowski-Górecki 2021-05-11 10:45 ` Marek Marczykowski-Górecki 2021-05-11 12:46 ` Durrant, Paul 2021-05-17 21:43 ` Marek Marczykowski-Górecki 2021-05-17 21:51 ` Michael Brown 2021-05-17 21:58 ` Marek Marczykowski-Górecki 2021-05-18 6:57 ` Paul Durrant 2021-05-18 9:18 ` Marek Marczykowski-Górecki [not found] ` <887f9533f5c54bfabfbff7231eb99b08@EX13D32EUC003.ant.amazon.com> [not found] ` <YKOMpXwcnr9QiXy8@mail-itl> [not found] ` <2c23e102b6254e42877eb1e8fe68a4f7@EX13D32EUC003.ant.amazon.com> 2021-05-18 10:42 ` Marek Marczykowski-Górecki
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=YJmBDpqQ12ZBGf58@mail-itl \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --subject='Re: [PATCH] xen-netback: Check for hotplug-status existence before watching' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).