Re: Regression with initramfs and nfsroot (appears to be in the dcache)

From: Patrick McLean
Date: Thu Nov 29 2012 - 20:04:43 EST

On 29/11/12 04:35 PM, Al Viro wrote:
> On Thu, Nov 29, 2012 at 04:19:51PM -0800, Patrick McLean wrote:
>>>> [ 8.821584] FH(0)]
>>>> [ 8.821586] FH(36)[01 00 07 01 89 00 00 00 00 00 00 00 e1 21 fe c4 9e 38 44 dc bf 1b d5 95 d6 76 d6 d9 a7 3c 1b 80 33 38 e3 62]
>>>> [ 8.821601] filename: proc
>>>
>>> *whoa*
>>>
>>> So we have zero entry->fh->size? No wonder it doesn't match... Which NFS
>>> version it is? entry->fh->size is set by nfs[34]_decode_dirent().
>>
>> This is nfs v3 over TCP on Linus git at commit e9296e89b85604862bd9ec2d54dc43edad775c0d with nfs-utils-1.2.6 userspace.
>
> So we have nfs3_decode_dirent(), stepping into
> /* In fact, a post_op_fh3: */
> p = xdr_inline_decode(xdr, 4);
> if (unlikely(p == NULL))
> goto out_overflow;
> if (*p != xdr_zero) {
> error = decode_nfs_fh3(xdr, entry->fh);
> if (unlikely(error)) {
> if (error == -E2BIG)
> goto out_truncated;
> return error;
> }
> } else
> zero_nfs_fh3(entry->fh);
> Interesting... Server-side that should've been produced by
> encode_entryplus_baggage(), which looks like failing compose_entry_fh()...
> which has explicit
> if (d_mountpoint(dchild))
> goto out;
> resulting in ENOENT on everything that's overmounted on server.
>
> Do you, by any chance, have the server really exporting its own root
> filesystem? Another thing to check: have nfs_prime_dcache() print
> filename.name of everything that fails nfs_same_entry() and has
> zero entry->fh->size, regardless of d_invalidate() results.

The server is running 3.6.6 and is just exporting a subdir of an xfs filesystem (which does not happen to be the root filesystem).

The client is running as a KVM guest on the machine that is serving the NFS. I am reproducing this by booting the guest via an initramfs, and doing
"ls /" at in single user mode.

I added a check that prints the filename.name of everything that fails nfs_same_file, and it appears to just be triggered by the same filesystems that
are triggering the WARN_ON, the relevant dmesg is below.

[ 9.495217] entry->fh->size is 0 on: proc
[ 9.495222] ------------[ cut here ]------------
[ 9.495230] WARNING: at fs/nfs/dir.c:464 nfs_readdir_page_filler+0x1ef/0x3eb()
[ 9.495232] Hardware name: Bochs
[ 9.495233] Modules linked in:
[ 9.495237] Pid: 655, comm: ls Not tainted 3.7.0-rc7+ #40
[ 9.495239] Call Trace:
[ 9.495247] [<ffffffff8108534c>] ? warn_slowpath_common+0x76/0x8a
[ 9.495250] [<ffffffff8117deb4>] ? nfs_readdir_page_filler+0x1ef/0x3eb
[ 9.495254] [<ffffffff8117e6cc>] ? nfs_readdir_xdr_to_array+0x1c0/0x22d
[ 9.495257] [<ffffffff8117e755>] ? nfs_readdir_filler+0x1c/0x6b
[ 9.495263] [<ffffffff810dca9a>] ? add_to_page_cache_lru+0x2c/0x36
[ 9.495266] [<ffffffff8117e739>] ? nfs_readdir_xdr_to_array+0x22d/0x22d
[ 9.495269] [<ffffffff810dcbe3>] ? do_read_cache_page+0x7d/0x12b
[ 9.495274] [<ffffffff811274f8>] ? sys_ioctl+0x7a/0x7a
[ 9.495277] [<ffffffff810dccc6>] ? read_cache_page+0x7/0x10
[ 9.495280] [<ffffffff8117e8d1>] ? nfs_readdir+0x12d/0x435
[ 9.495285] [<ffffffff8118e69b>] ? nfs3_xdr_dec_create3res+0xc5/0xc5
[ 9.495288] [<ffffffff811274f8>] ? sys_ioctl+0x7a/0x7a
[ 9.495291] [<ffffffff811274f8>] ? sys_ioctl+0x7a/0x7a
[ 9.495294] [<ffffffff811277b3>] ? vfs_readdir+0x6c/0xa7
[ 9.495298] [<ffffffff811278da>] ? sys_getdents+0x7e/0xdc
[ 9.495302] [<ffffffff814ac829>] ? system_call_fastpath+0x16/0x1b
[ 9.495304] ---[ end trace e502c5d56c594e85 ]---
[ 9.495306] FH(0)]
[ 9.495308] FH(36)[01 00 07 01 89 00 00 00 00 00 00 00 e1 21 fe c4 9e 38 44 dc bf 1b d5 95 d6 76 d6 d9 a7 3c 1b 80 33 38 e3 62]
[ 9.495323] filename: proc
[ 9.495330] entry->fh->size is 0 on: dev
[ 9.495332] ------------[ cut here ]------------
[ 9.495335] WARNING: at fs/nfs/dir.c:464 nfs_readdir_page_filler+0x1ef/0x3eb()
[ 9.495336] Hardware name: Bochs
[ 9.495337] Modules linked in:
[ 9.495340] Pid: 655, comm: ls Tainted: G W 3.7.0-rc7+ #40
[ 9.495341] Call Trace:
[ 9.495345] [<ffffffff8108534c>] ? warn_slowpath_common+0x76/0x8a
[ 9.495348] [<ffffffff8117deb4>] ? nfs_readdir_page_filler+0x1ef/0x3eb
[ 9.495351] [<ffffffff8117e6cc>] ? nfs_readdir_xdr_to_array+0x1c0/0x22d
[ 9.495354] [<ffffffff8117e755>] ? nfs_readdir_filler+0x1c/0x6b
[ 9.495358] [<ffffffff810dca9a>] ? add_to_page_cache_lru+0x2c/0x36
[ 9.495361] [<ffffffff8117e739>] ? nfs_readdir_xdr_to_array+0x22d/0x22d
[ 9.495364] [<ffffffff810dcbe3>] ? do_read_cache_page+0x7d/0x12b
[ 9.495368] [<ffffffff811274f8>] ? sys_ioctl+0x7a/0x7a
[ 9.495371] [<ffffffff810dccc6>] ? read_cache_page+0x7/0x10
[ 9.495373] [<ffffffff8117e8d1>] ? nfs_readdir+0x12d/0x435
[ 9.495377] [<ffffffff8118e69b>] ? nfs3_xdr_dec_create3res+0xc5/0xc5
[ 9.495380] [<ffffffff811274f8>] ? sys_ioctl+0x7a/0x7a
[ 9.495383] [<ffffffff811274f8>] ? sys_ioctl+0x7a/0x7a
[ 9.495387] [<ffffffff811277b3>] ? vfs_readdir+0x6c/0xa7
[ 9.495390] [<ffffffff811278da>] ? sys_getdents+0x7e/0xdc
[ 9.495393] [<ffffffff814ac829>] ? system_call_fastpath+0x16/0x1b
[ 9.495395] ---[ end trace e502c5d56c594e86 ]---
[ 9.495396] FH(0)]
[ 9.495397] FH(36)[01 00 07 01 89 00 00 00 00 00 00 00 e1 21 fe c4 9e 38 44 dc bf 1b d5 95 d6 76 d6 d9 85 00 00 40 d6 39 e0 7d]
[ 9.495412] filename: dev
[ 9.495422] entry->fh->size is 0 on: sys
[ 9.495423] ------------[ cut here ]------------
[ 9.495426] WARNING: at fs/nfs/dir.c:464 nfs_readdir_page_filler+0x1ef/0x3eb()
[ 9.495427] Hardware name: Bochs
[ 9.495428] Modules linked in:
[ 9.495430] Pid: 655, comm: ls Tainted: G W 3.7.0-rc7+ #40
[ 9.495431] Call Trace:
[ 9.495435] [<ffffffff8108534c>] ? warn_slowpath_common+0x76/0x8a
[ 9.495438] [<ffffffff8117deb4>] ? nfs_readdir_page_filler+0x1ef/0x3eb
[ 9.495441] [<ffffffff8117e6cc>] ? nfs_readdir_xdr_to_array+0x1c0/0x22d
[ 9.495444] [<ffffffff8117e755>] ? nfs_readdir_filler+0x1c/0x6b
[ 9.495448] [<ffffffff810dca9a>] ? add_to_page_cache_lru+0x2c/0x36
[ 9.495450] [<ffffffff8117e739>] ? nfs_readdir_xdr_to_array+0x22d/0x22d
[ 9.495454] [<ffffffff810dcbe3>] ? do_read_cache_page+0x7d/0x12b
[ 9.495457] [<ffffffff811274f8>] ? sys_ioctl+0x7a/0x7a
[ 9.495460] [<ffffffff810dccc6>] ? read_cache_page+0x7/0x10
[ 9.495463] [<ffffffff8117e8d1>] ? nfs_readdir+0x12d/0x435
[ 9.495466] [<ffffffff8118e69b>] ? nfs3_xdr_dec_create3res+0xc5/0xc5
[ 9.495470] [<ffffffff811274f8>] ? sys_ioctl+0x7a/0x7a
[ 9.495473] [<ffffffff811274f8>] ? sys_ioctl+0x7a/0x7a
[ 9.495476] [<ffffffff811277b3>] ? vfs_readdir+0x6c/0xa7
[ 9.495479] [<ffffffff811278da>] ? sys_getdents+0x7e/0xdc
[ 9.495482] [<ffffffff814ac829>] ? system_call_fastpath+0x16/0x1b
[ 9.495484] ---[ end trace e502c5d56c594e87 ]---
[ 9.495485] FH(0)]
[ 9.495486] FH(36)[01 00 07 01 89 00 00 00 00 00 00 00 e1 21 fe c4 9e 38 44 dc bf 1b d5 95 d6 76 d6 d9 a3 0e 00 40 42 57 d3 90]
[ 9.495511] filename: sys
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