Date:	Fri, 14 Aug 2015 10:07:19 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Sven Geggus <lists@...hsschwanzdomain.de>
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

Sven Geggus <lists@...hsschwanzdomain.de> writes:

> 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.

That does sound interesting.

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

My educated but unsupported guess would be that there is likely
something funny going on with attributes somewhere like there was with
nfs_prime_dcache.

At a quick look the failure possibilities are:
nfs_lookup_verify_inode failing,
NFS_STALE(inode) being true,
NFS_PROTO(dir)->lookup failing,
nfs_compare_fh failing,
nfs_refresh_inode failing,

I expect what needs to happen now is to drill down into
nfs_lookup_revalidate especially into the branches that can lead to
out_bad and add some print statments so that it becomes clear just
what conditions are causing nfs_lookup_invalidate to fail.

I don't have a clue what the issue would be but I would start with
something like the patch below.  That will help narrow it down even
further.  And there are still enough possibilities that I don't think
anyone has enough information yet to figure out what is going on from
first principles.

Eric

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 547308a5ec6f..97c70c887b23 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1167,7 +1167,7 @@ static int nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
 		return -ECHILD;
 
 	if (NFS_STALE(inode))
-		goto out_bad;
+		goto out_bad1;
 
 	error = -ENOMEM;
 	fhandle = nfs_alloc_fhandle();
@@ -1183,11 +1183,11 @@ static int nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
 	error = NFS_PROTO(dir)->lookup(dir, &dentry->d_name, fhandle, fattr, label);
 	trace_nfs_lookup_revalidate_exit(dir, dentry, flags, error);
 	if (error)
-		goto out_bad;
+		goto out_bad2;
 	if (nfs_compare_fh(NFS_FH(inode), fhandle))
-		goto out_bad;
+		goto out_bad3;
 	if ((error = nfs_refresh_inode(inode, fattr)) != 0)
-		goto out_bad;
+		goto out_bad4;
 
 	nfs_setsecurity(inode, fattr, label);
 
@@ -1210,6 +1210,8 @@ out_set_verifier:
 			__func__, dentry);
 	return 1;
 out_zap_parent:
+	dfprintk(LOOKUPCACHE "NFS: %s(%pd2): nfs_lookup_verify_inode() failed\n",
+		 __func__, dentry);
 	nfs_zap_caches(dir);
  out_bad:
 	WARN_ON(flags & LOOKUP_RCU);
@@ -1233,6 +1235,22 @@ out_zap_parent:
 	dfprintk(LOOKUPCACHE, "NFS: %s(%pd2) is invalid\n",
 			__func__, dentry);
 	return 0;
+out_bad1:
+	dfprintk(LOOKUPCACHE, "NFS: %s(%pd2): NFS_STALE(inode)\n",
+		 __func__, dentry);
+	goto out_bad;
+out_bad2:
+	dfprintk(LOOKUPCACHE, "NFS: %s(%pd2): NFS_PROTO(dir)->lookup -> %u\n",
+		 __func__, dentry, error);
+	goto out_bad;
+out_bad3:
+	dfprintk(LOOKUPCACHE, "NFS: %s(%pd2): nfs_compare_fh() failed\n",
+		 __func__, dentry);
+	goto out_bad;
+out_bad4:
+	dfprintk(LOOKUPCACHE "NFS: %s(%pd2): nfs_refresh_inode() -> %u\n",
+		 __func__, dentry, error);
+	goto out_bad;
 out_error:
 	WARN_ON(flags & LOOKUP_RCU);
 	nfs_free_fattr(fattr);

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