linux-kernel - Re: (NFS) BUG: at page-writeback.c:829 [Was: 2.6.22-rc1-mm1]

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Date:	Wed, 16 May 2007 23:06:59 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Trond Myklebust <trond.myklebust@....uio.no>
CC:	Jiri Slaby <jirislaby@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: (NFS) BUG: at page-writeback.c:829 [Was: 2.6.22-rc1-mm1]

Trond Myklebust wrote:
> On Wed, 2007-05-16 at 22:39 +1000, Nick Piggin wrote:
> 
>>> =======================
>>>BUG: at /local/xslaby/xxx/mm/page-writeback.c:829 __set_page_dirty_nobuffers()
>>> [<c010531e>] dump_trace+0x1ce/0x200
>>> [<c010536a>] show_trace_log_lvl+0x1a/0x30
>>> [<c0106012>] show_trace+0x12/0x20
>>> [<c0106086>] dump_stack+0x16/0x20
>>> [<c015566d>] __set_page_dirty_nobuffers+0x11d/0x130
>>> [<f8b1fc5b>] nfs_updatepage+0x7b/0x200 [nfs]
>>> [<f8b156df>] nfs_commit_write+0x2f/0x50 [nfs]
>>> [<c0150911>] generic_file_buffered_write+0x2a1/0x660
>>> [<c0150f52>] __generic_file_aio_write_nolock+0x282/0x520
>>> [<c0151252>] generic_file_aio_write+0x62/0xd0
>>> [<f8b15def>] nfs_file_write+0xef/0x1c0 [nfs]
>>> [<c01715e0>] do_sync_write+0xd0/0x110
>>> [<c0171e04>] vfs_write+0x94/0x130
>>> [<c017248d>] sys_write+0x3d/0x70
>>> [<c01040e8>] syscall_call+0x7/0xb
>>> [<b7eb7b3e>] 0xb7eb7b3e
>>> =======================
>>
>>This one is NFS, setting the page dirty while it is not uptodate. Trond,
>>is this because NFS keeps track of dirty regions of the page with private
>>data? It might make sense to avoid this warning if PagePrivate is set...
>>would that fix the NFS case?
> 
> 
> Ah... You put an extra WARN_ON(!PageUptodate(page)). err=-ENOCOFFEE, I
> missed that...
> 
> 
> So yes, in order to avoid having to read the page in when we just want
> to write data, NFS does this kind of tracking. I dunno if your fix to
> change it to !PagePrivate(page) && !PageUptodate(page) is right though.
> It will indeed fix the NFS case, but the block system uses PagePrivate()
> pretty extensively for its own nefarious ends (tracking page buffers).

I think that's OK: the block layer is similarly happy to mark a !uptodate
page dirty if it has buffers, for similar reasons... Anyway, it won't use
this particular path when buffers are attached, and I've put similar
debugging stuff in the set_page_dirty_buffers part.

-- 
SUSE Labs, Novell Inc.
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