linux-kernel - Re: nfs-root: destructive call to __detach

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Date:	Fri, 14 Aug 2015 13:01:40 +0200
From:	Sven Geggus <lists@...hsschwanzdomain.de>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-kernel@...r.kernel.org, trond.myklebust@...marydata.com,
	linux-nfs@...r.kernel.org
Subject: Re: nfs-root: destructive call to __detach_mounts /dev

On 31-07-15 09:27 Eric W. Biederman wrote:

> I have added the linux-nfs list to hopefully add a wider interested
> audience.

... which made your mail get burried in my linux-nfs mailinglist folder :(
But I finaly found it.

> If what is being revalidated is a mount point nfs4_lookup_revalidate
> calls nfs_lookup_revalidate.  So nfs_lookup_revalidate is the only
> interesting function.

OK.

> I don't understand the what nfs_lookup_revalidate is doing particularly
> well.  

Neither do I.

Here is what I get from a broken machine (Kernel 4.1.5) using
"rpcdebug -m nfs -s lookupcache":

The mountpoint which got unmounted in this case is /proc not /dev, but the
stack-trace points to the same place.

Aug 14 11:49:37 banthonytwarog kernel: NFS: nfs_lookup_revalidate(/proc) is valid
Aug 14 11:49:37 banthonytwarog kernel: NFS: nfs_lookup_revalidate(/proc) is invalid
Aug 14 11:49:37 banthonytwarog kernel: NFSROOT __detach_mounts: proc
Aug 14 11:49:37 banthonytwarog kernel: CPU: 2 PID: 28350 Comm: modtrack Tainted: P        W  O    4.1.5-lomac3-00293-gfdd763a #6
Aug 14 11:49:37 banthonytwarog kernel: Hardware name: System manufacturer System Product Name/P8H67, BIOS 3506 03/02/2012
Aug 14 11:49:37 banthonytwarog kernel: ffff8800d9b93bb8 ffff8800d9b93b78 ffffffff81560488 00000000446c446c
Aug 14 11:49:37 banthonytwarog kernel: ffff88040c427d98 ffff8800d9b93b98 ffffffff81106d36 00000000000000a2
Aug 14 11:49:37 banthonytwarog kernel: ffff88040c427d98 ffff8800d9b93be8 ffffffff810ffc0c 00000000d9b93c08
Aug 14 11:49:37 banthonytwarog kernel: Call Trace:
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff81560488>] dump_stack+0x4c/0x6e
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff81106d36>] __detach_mounts+0x20/0xdf
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810ffc0c>] d_invalidate+0x9a/0xc8
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810f6b60>] lookup_fast+0x1f5/0x26f
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810f5a44>] ? __inode_permission+0x37/0x95
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810f7c02>] link_path_walk+0x204/0x749
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810f4db2>] ? terminate_walk+0x10/0x2e
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810f75e7>] ? do_last.isra.43+0x8b6/0x9fb
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810f846f>] path_init+0x328/0x337
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810f919a>] path_openat+0x1b0/0x53e
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810fa073>] do_filp_open+0x75/0x85
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff8110427b>] ? __alloc_fd+0xdd/0xef
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810ec9b3>] do_sys_open+0x146/0x1d5
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810d1c5c>] ? vm_munmap+0x4b/0x59
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff810eca5b>] SyS_open+0x19/0x1b
Aug 14 11:49:37 banthonytwarog kernel: [<ffffffff81565897>] system_call_fastpath+0x12/0x6a

I suppose, that the first two lines are particularly interesting as we have
"is valid" and a fraction of a second later we have "is invalid" at the same
mountpoint.

To me this looks like a job for the NFS client maintainers now, right?

Sven

-- 
Exploits and holes are a now a necessary protection against large
corporate interests. (Alan Cox)

/me is giggls@...net, http://sven.gegg.us/ on the Web
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