Messages in this thread | | | Date | Mon, 30 Oct 2023 13:45:33 +0800 | Subject | Re: [PATCH v4 2/6] mounts: keep list of mounts in an rbtree | From | Ian Kent <> |
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On 30/10/23 13:37, Ian Kent wrote: > On 28/10/23 09:36, Ian Kent wrote: >> On 27/10/23 16:17, Miklos Szeredi wrote: >>> On Fri, Oct 27, 2023 at 5:12 AM Ian Kent <raven@themaw.net> wrote: >>>> On 25/10/23 22:02, Miklos Szeredi wrote: >>>>> The mnt.mnt_list is still used to set up the mount tree and for >>>>> propagation, but not after the mount has been added to a >>>>> namespace. Hence >>>>> mnt_list can live in union with rb_node. Use MNT_ONRB mount flag to >>>>> validate that the mount is on the correct list. >>>> Is that accurate, propagation occurs at mount and also at umount. >>> When propagating a mount, the new mount's mnt_list is used as a head >>> for the new propagated mounts. These are then moved to the rb tree by >>> commit_tree(). >>> >>> When umounting there's a "to umount" list called tmp_list in >>> umount_tree(), this list is used to collect direct umounts and then >>> propagated umounts. The direct umounts are added in umount_tree(), >>> the propagated ones umount_one(). >>> >>> Note: umount_tree() can be called on a not yet finished mount, in that >>> case the mounts are still on mnt_list, so umount_tree() needs to deal >>> with both. >>> >>>> IDG how the change to umount_one() works, it looks like umount_list() >>>> >>>> uses mnt_list. It looks like propagate_umount() is also using >>>> mnt_list. >>>> >>>> >>>> Am I missing something obvious? >>> So when a mount is part of a namespace (either anonymous or not) it is >>> on the rb tree, when not then it can temporarily be on mnt_list. >>> MNT_ONRB flag is used to validate that the mount is on the list that >>> we expect it to be on, but also to detect the case of the mount setup >>> being aborted. >>> >>> We could handle the second case differently, since we should be able >>> to tell when we are removing the mount from a namespace and when we >>> are aborting a mount, but this was the least invasive way to do this. >> >> Thanks for the explanation, what you've said is essentially what I >> >> understood reading the series. >> >> >> But I still haven't quite got this so I'll need to spend more time >> >> on this part of the patch series. >> >> >> That's not a problem, ;). > > After cloning your git tree and looking in there I don't see what > > I was concerned about so I think I was confused by obscurity by > > diff rather than seeing a real problem, ;) > > > Still that union worries me a little bit so I'll keep looking at > > the code for a while.
Is fs/namespace.c:iterate_mounts() a problem?
It's called from:
1) ./kernel/audit_tree.c:709: if (iterate_mounts(compare_root, 2) ./kernel/audit_tree.c:839: err = iterate_mounts(tag_mount, tree, mnt); 3) ./kernel/audit_tree.c:917: failed = iterate_mounts(tag_mount, tree, tagged);
From functions 1) audit_trim_trees(), 2) audit_add_tree_rule() and
3) audit_tag_tree().
> > >> >> >> Ian >> >>> >>> Thanks, >>> Miklos >>> >> >
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