From: NeilBrown <neilb-IBi9RG/b67k@public.gmane.org> To: "J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org> Cc: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, "linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Trond Myklebust <trond.myklebust-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org> Subject: Re: export table lookup: was [PATCH 10/10 v7] nfsd: Allows user un-mounting filesystem where nfsd exports base on Date: Fri, 24 Jul 2015 09:46:57 +1000 [thread overview] Message-ID: <20150724094657.0ca793b4@noble> (raw) In-Reply-To: <20150722150840.GH22718-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org> On Wed, 22 Jul 2015 11:08:40 -0400 "J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org> wrote: > I've had this nagging todo to work out if there are other interesting > consequences of the fact that the cache is internally keyed on one thing > and appears to mountd to be keyed on another. (And that there's a > complicated many<->many relationship between those two things.) But I > haven't gotten to it. Could be all unlikely corner cases, for all I > know. Even corner cases are worth resolving - and you got me interested now:-) I think the distinction between pathnames and mnt+dentry is not quite the important one. I think mnt+dentry is the primary object - it is what a filehandle maps to and what a pathname maps to. The problem is that some mnt+dentry pairs do not have matching path names. If nfsd gets hold of one of these pairs, it shouldn't try asking mountd about it because there is no way to ask the question, and even if there was it isn't clear there is any way for mountd to answer. If think that nfsd should assume that any such mountpoint is not exported. So something vaguely like: diff --git a/fs/dcache.c b/fs/dcache.c index 5c8ea15e73a5..a0651872ae8e 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2943,6 +2943,12 @@ restart: if (error) break; + if (unlikely(d_mountpoint(dentry))) { + struct mount *mounted = __lookup_mnt(vfsmnt, dentry); + if (mounted) + prepend(&bptr, &blen, "//(unreachable)",15); + } + dentry = parent; } if (!(seq & 1)) Would mean that if I # cd /tmp/a/b/c # mount --bind /etc /tmp/a # /bin/pwd I get /tmp//(unreachable)/a/b/c would could be checked for by nfsd to decide that there is no point asking user-space. I'm not at all certain that this is a good interface (or that the code isn't racy) - it is just a proof-of-concept. We should probably place the (unreachable) at the front rather than in the middle. Does that seem like a reasonable approach from your understanding of the problem? Thanks, NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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From: NeilBrown <neilb@suse.com> To: "J. Bruce Fields" <bfields@fieldses.org> Cc: Kinglong Mee <kinglongmee@gmail.com>, Al Viro <viro@zeniv.linux.org.uk>, "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>, linux-fsdevel@vger.kernel.org, Trond Myklebust <trond.myklebust@primarydata.com> Subject: Re: export table lookup: was [PATCH 10/10 v7] nfsd: Allows user un-mounting filesystem where nfsd exports base on Date: Fri, 24 Jul 2015 09:46:57 +1000 [thread overview] Message-ID: <20150724094657.0ca793b4@noble> (raw) In-Reply-To: <20150722150840.GH22718@fieldses.org> On Wed, 22 Jul 2015 11:08:40 -0400 "J. Bruce Fields" <bfields@fieldses.org> wrote: > I've had this nagging todo to work out if there are other interesting > consequences of the fact that the cache is internally keyed on one thing > and appears to mountd to be keyed on another. (And that there's a > complicated many<->many relationship between those two things.) But I > haven't gotten to it. Could be all unlikely corner cases, for all I > know. Even corner cases are worth resolving - and you got me interested now:-) I think the distinction between pathnames and mnt+dentry is not quite the important one. I think mnt+dentry is the primary object - it is what a filehandle maps to and what a pathname maps to. The problem is that some mnt+dentry pairs do not have matching path names. If nfsd gets hold of one of these pairs, it shouldn't try asking mountd about it because there is no way to ask the question, and even if there was it isn't clear there is any way for mountd to answer. If think that nfsd should assume that any such mountpoint is not exported. So something vaguely like: diff --git a/fs/dcache.c b/fs/dcache.c index 5c8ea15e73a5..a0651872ae8e 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2943,6 +2943,12 @@ restart: if (error) break; + if (unlikely(d_mountpoint(dentry))) { + struct mount *mounted = __lookup_mnt(vfsmnt, dentry); + if (mounted) + prepend(&bptr, &blen, "//(unreachable)",15); + } + dentry = parent; } if (!(seq & 1)) Would mean that if I # cd /tmp/a/b/c # mount --bind /etc /tmp/a # /bin/pwd I get /tmp//(unreachable)/a/b/c would could be checked for by nfsd to decide that there is no point asking user-space. I'm not at all certain that this is a good interface (or that the code isn't racy) - it is just a proof-of-concept. We should probably place the (unreachable) at the front rather than in the middle. Does that seem like a reasonable approach from your understanding of the problem? Thanks, NeilBrown
next prev parent reply other threads:[~2015-07-23 23:46 UTC|newest] Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-07-11 12:46 [PATCH 00/10 v7] NFSD: Pin to vfsmount for nfsd exports cache Kinglong Mee 2015-07-11 12:46 ` Kinglong Mee 2015-07-11 12:49 ` [PATCH 05/10 v7] sunrpc: Store cache_detail in seq_file's private, directly Kinglong Mee 2015-07-11 12:49 ` [PATCH 06/10 v7] sunrpc/nfsd: Remove redundant code by exports seq_operations functions Kinglong Mee [not found] ` <55A11010.6050005-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 2015-07-11 12:47 ` [PATCH 01/10 v7] fs_pin: Initialize value for fs_pin explicitly Kinglong Mee 2015-07-11 12:47 ` Kinglong Mee 2015-07-11 12:47 ` [PATCH 02/10 v7] fs_pin: Export functions for specific filesystem Kinglong Mee 2015-07-11 12:47 ` Kinglong Mee 2015-07-11 12:48 ` [PATCH 03/10 v7] path: New helpers path_get_pin/path_put_unpin for path pin Kinglong Mee 2015-07-11 12:48 ` Kinglong Mee 2015-07-11 12:48 ` [PATCH 04/10 v7] fs: New helper legitimize_mntget() for getting a legitimize mnt Kinglong Mee 2015-07-11 12:48 ` Kinglong Mee 2015-07-11 12:50 ` [PATCH 07/10 v7] sunrpc: Switch to using list_head instead single list Kinglong Mee 2015-07-11 12:50 ` Kinglong Mee [not found] ` <55A11112.8080502-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 2015-07-11 12:54 ` Christoph Hellwig 2015-07-11 12:54 ` Christoph Hellwig 2015-07-13 1:30 ` NeilBrown 2015-07-13 8:27 ` Kinglong Mee 2015-07-13 8:27 ` Kinglong Mee 2015-07-11 12:51 ` [PATCH 09/10 v7] sunrpc: Support get_ref/put_ref for reference change in cache_head Kinglong Mee 2015-07-11 12:51 ` Kinglong Mee 2015-07-11 12:52 ` [PATCH 10/10 v7] nfsd: Allows user un-mounting filesystem where nfsd exports base on Kinglong Mee 2015-07-11 12:52 ` Kinglong Mee [not found] ` <55A111A8.2040701-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 2015-07-13 3:39 ` NeilBrown 2015-07-13 3:39 ` NeilBrown 2015-07-13 4:02 ` Al Viro [not found] ` <20150713040258.GM17109-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org> 2015-07-13 5:19 ` NeilBrown 2015-07-13 5:19 ` NeilBrown 2015-07-13 6:02 ` Al Viro 2015-07-13 6:02 ` Al Viro 2015-07-13 4:20 ` NeilBrown 2015-07-13 4:45 ` Al Viro 2015-07-13 4:45 ` Al Viro [not found] ` <20150713044553.GN17109-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org> 2015-07-13 5:21 ` NeilBrown 2015-07-13 5:21 ` NeilBrown 2015-07-13 6:02 ` NeilBrown 2015-07-13 6:02 ` NeilBrown 2015-07-13 6:08 ` Al Viro 2015-07-13 6:08 ` Al Viro [not found] ` <20150713060802.GP17109-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org> 2015-07-13 6:32 ` NeilBrown 2015-07-13 6:32 ` NeilBrown 2015-07-13 6:43 ` Al Viro 2015-07-13 6:43 ` Al Viro 2015-07-15 3:49 ` NeilBrown 2015-07-15 4:57 ` Al Viro 2015-07-15 4:57 ` Al Viro 2015-07-15 6:51 ` NeilBrown 2015-07-24 2:05 ` NeilBrown 2015-07-27 2:28 ` Kinglong Mee [not found] ` <55B59764.1020506-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 2015-07-27 2:51 ` NeilBrown 2015-07-27 2:51 ` NeilBrown 2015-07-27 3:17 ` Kinglong Mee 2015-07-15 21:07 ` J. Bruce Fields 2015-07-15 21:07 ` J. Bruce Fields [not found] ` <20150715210756.GE21669-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org> 2015-07-15 23:40 ` NeilBrown 2015-07-15 23:40 ` NeilBrown 2015-07-16 20:51 ` J. Bruce Fields 2015-07-16 20:51 ` J. Bruce Fields [not found] ` <20150716205148.GC10673-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org> 2015-07-21 21:58 ` NeilBrown 2015-07-21 21:58 ` NeilBrown 2015-07-22 15:08 ` J. Bruce Fields 2015-07-22 15:08 ` J. Bruce Fields [not found] ` <20150722150840.GH22718-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org> 2015-07-23 23:46 ` NeilBrown [this message] 2015-07-23 23:46 ` export table lookup: was " NeilBrown 2015-07-24 19:48 ` J. Bruce Fields 2015-07-24 19:48 ` J. Bruce Fields 2015-07-25 0:40 ` NeilBrown 2015-07-11 12:51 ` [PATCH 08/10 v7] sunrpc: New helper cache_delete_entry for deleting cache_head directly Kinglong Mee
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