From: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Subject: [BUG] problem with nfs_invaildate_page
Date: Fri, 24 Aug 2007 16:43:46 +0900
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Hi,

I got the following BUG in nfs_inode_add_request() when I was using
eCryptfs on NFS. (Don't ask me why I was doing that)

------------[ cut here ]------------
kernel BUG at fs/nfs/write.c:387!
invalid opcode: 0000 [#1]
PREEMPT SMP
Modules linked in: cbc md5 aes ecb blkcipher cryptomgr crypto_algapi ecryptfs
nfs iscsi_tcp libiscsi scsi_transport_iscsi nfsd exportfs lockd nfs_acl sunrpc
nbd md_mod dm_snapshot dm_mirror dm_mod video output
CPU:    5
EIP:    0060:[<f90113e2>]    Not tainted VLI
EFLAGS: 00010246   (2.6.23-rc3 #5)
EIP is at nfs_writepage_setup+0xc8/0x305 [nfs]
eax: ffffffef   ebx: ffffffef   ecx: 00000000   edx: f776a6c8
esi: f776a700   edi: f3392680   ebp: f6489c04   esp: f6489bc4
ds: 007b   es: 007b   fs: 00d8  gs: 0033  ss: 0068
Process dd (pid: 4260, ti=f6488000 task=f5719500 task.ti=f6488000)
Stack: 00000000 00001000 dd751a4f 730e4905 00000000 c404e0c0 f5a86a80 f33927e4
       f3392774 00000000 f6489bf4 c029e298 00000000 f6812780 00000000 c404e0c0
       f6489c44 f9011b8c 00001000 00001000 00000010 fff2b000 f6489d08 00000246
Call Trace:
 [<c01082d6>] show_trace_log_lvl+0x1a/0x2f
 [<c0108388>] show_stack_log_lvl+0x9d/0xa5
 [<c0108581>] show_registers+0x1f1/0x332
 [<c01087dd>] die+0x11b/0x250
 [<c0480cd0>] do_trap+0x8a/0xa3
 [<c0108bd1>] do_invalid_op+0x88/0x92
 [<c0480a9a>] error_code+0x72/0x78
 [<f9011b8c>] nfs_updatepage+0x14d/0x1b3 [nfs]
 [<f9008f93>] nfs_commit_write+0x29/0x39 [nfs]
 [<f8fe0ae5>] ecryptfs_commit_lower_page+0x26/0x6b [ecryptfs]
 [<f8fe2675>] ecryptfs_write_out_page+0x28/0x73 [ecryptfs]
 [<f8fe32ac>] ecryptfs_encrypt_page+0x3a4/0x419 [ecryptfs]
 [<f8fe12e0>] ecryptfs_commit_write+0x1ba/0x31f [ecryptfs]
 [<c015c1ab>] generic_file_buffered_write+0x3a6/0x54e
 [<c015c793>] __generic_file_aio_write_nolock+0x440/0x493
 [<c015c83c>] generic_file_aio_write+0x56/0xb4
 [<c0178a7c>] do_sync_write+0xc5/0x102
 [<c017923e>] vfs_write+0xaf/0x138
 [<c0179806>] sys_write+0x3d/0x61
 [<c010719a>] syscall_call+0x7/0xb
 =======================
Code: 00 00 00 f0 0f ba 6e 28 00 19 c0 8b 7d e0 81 ef f4 00 00 00 8b 56
14 8b 45 e0 83 e8 1c 89 f1 e8 50 db 29 c7 89 c3 83 f8 ef 75 04 <0f> 0b
eb fe 85 c0 75 4e 83 bf e8 00 00 00 00 75 10 8b 45 e0 e8
EIP: [<f90113e2>] nfs_writepage_setup+0xc8/0x305 [nfs] SS:ESP 0068:f6489bc4

As you may have guessed, the BUG shows a collision of nfs_page in a nfs
page tree.  That is, there is a case that nfs_page remains even if 
the requested page is removed from page cache.

static int nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
{
        struct nfs_inode *nfsi = NFS_I(inode);
        int error;

        error = radix_tree_insert(&nfsi->nfs_page_tree, req->wb_index, req);
        BUG_ON(error == -EEXIST);
        ...
}

By some tests, it turned out to be a discordance between 
nfs_invalidate_page() and truncate_inode_pages() in recent kernels.

In kernel 2.6.20, truncate_complete_page() was changed to clear dirty flag
from the removing page just before calling a_ops->invalidatepage().
As a result, nfs_wb_page_priority(), which is called from nfs_invalidate_page(),
get to skip nfs_writepage_locked() that starts to write dirty pages.

int nfs_wb_page_priority(struct inode *inode, struct page *page, int how)
{
	...
	if (clear_page_dirty_for_io(page)) {
		ret = nfs_writepage_locked(page, &wbc);
		if (ret < 0)
			goto out;
	}
	if (!PagePrivate(page))
		return 0;
	ret = nfs_sync_mapping_wait(page->mapping, &wbc, how);
 	...
}

Since nfs_sync_mapping_wait() does not care for non-dirty, unwritten,
and uncommitted pages, their nfs_page get into orphans.
It seems to need some sort of change to handle unwritten non-dirty
pages.

For reference, I will show the way to reproduce the BUG using
eCryptfs below.  I tried other way, but I couldn't find simpler
way not requiring eCryptfs so far.

 # mount -t nfs server:/pub /nfs
 # mount -t ecryptfs -o cipher=aes,ecryptfs_key_bytes=16 /nfs /secret
 # dd if=/dev/zero of=/secret/aaa bs=4096 count=1
 # dd if=/dev/zero of=/secret/aaa bs=4096 count=1

These procedures do truncate an unwritten NFS page.
Note that overwritting without use of eCryptfs doesn't reproduce 
the problem because it calls nfs_setattr() and forces the pages 
to be written back.

Cheers,
Ryusuke Konishi

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