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From: Dmitry Monakhov <dmonakhov@openvz.org>
To: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       linux-nfs@vger.kernel.org
Subject: Re: [PATCH] nfs: clear_commit_release incorrectly handle truncated page
References: <87hbpzhqlp.fsf@openvz.org> <1265123045.3177.21.camel@localhost>
	<87eil3pszw.fsf@openvz.org> <1265124999.3177.27.camel@localhost>
Date: Tue, 02 Feb 2010 18:56:27 +0300
In-Reply-To: <1265124999.3177.27.camel@localhost> (Trond Myklebust's message
	of "Tue, 02 Feb 2010 10:36:39 -0500")
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Trond Myklebust <trond.myklebust@fys.uio.no> writes:

> On Tue, 2010-02-02 at 18:17 +0300, Dmitry Monakhov wrote: 
>> Trond Myklebust <trond.myklebust@fys.uio.no> writes:
>> 
>> > On Tue, 2010-02-02 at 13:36 +0300, Dmitry Monakhov wrote: 
>> >> After page was truncated it lost it's mapping, this result in null
>> >> pointer dereference on bdi_stat update. In fact we have to decrement
>> >> bdi_stat even for truncated pages, so let's pass correct mapping in
>> >> function arguments. Patch against linux-2.6
>> >> ##TEST_CASE
>> >> /*
>> >> Tast case for bug in nfs_clear_request_commit()
>> >> caused by null pointer dereference in case of truncated page.
>> >> It takes less than 10 minutes to reproduce the bug.
>> >
>> > Something is wrong here. nfs_release_page() returns '0' if the 
>> > page has an associated write request (i.e. PagePrivate is set), and so
>> > both invalidate_complete_page() and invalidate_complete_page2() will
>> > fail.
>> >
>> > So what is truncating the page?
>> truncate_inode_page()
>>   truncate_complete_page()
>>     if (page_has_private(page))
>>        do_invalidatepage()
>>          ->nfs_invalidate_page()
>
> do_invalidate_page() is called before remove_from_page_cache(), so
> page->mapping should still be set.
Yes nfs_invalidate_page() happens before, but nfs_clear_commit_release()
is called from rpc task after page was removed from page-cache.
I've add following debug code in to nfs_clear_commit_release()
+ printk("page private index flags")
+ BUG_ON(!page->mapping);
And have got following output:

 page:c5c790e0 private:f109b700  index:97656 fl:8000082c
 ------------[ cut here ]------------
 kernel BUG at fs/nfs/write.c:456!
 invalid opcode: 0000 [#1] SMP 
 last sysfs file: /sys/devices/pci0000:00/0000:00:1b.0/sound/card0/controlC0/uevent
 Modules linked in: nfs lockd nfs_acl auth_rpcgss sunrpc binfmt_misc kvm_intel kvm radeon ttm drm_kms_helper drm i2c_algo_bit quota_v2 quota_tree snd_hda_codec_analog snd_hda_intel snd_hda_codec snd_pcm_oss snd_mixer_oss snd_pcm snd_seq_dummy thinkpad_acpi snd_seq_oss snd_seq_midi snd_rawmidi snd_seq_midi_event arc4 snd_seq iwl3945 snd_timer iwlcore snd_seq_device iptable_filter tpm_tis snd pcmcia mac80211 yenta_socket soundcore ip_tables tpm led_class psmouse rsrc_nonstatic snd_page_alloc tpm_bios x_tables nvram serio_raw sierra cfg80211 pcmcia_core raid10 raid456 async_raid6_recov async_pq raid6_pq async_xor xor async_memcpy async_tx raid1 raid0 multipath linear intel_agp video output e1000e agpgart [last unloaded: nfs]
 
 Pid: 3646, comm: nfsiod Not tainted 2.6.33-rc4 #47 2623DDU/2623DDU
 EIP: 0060:[<fc87ce57>] EFLAGS: 00010282 CPU: 0
 EIP is at nfs_clear_request_commit+0xf7/0x100 [nfs]
 EAX: 00000049 EBX: c5c790e0 ECX: c05a9a8f EDX: 05764000
 ESI: f10d9c00 EDI: fc8968f8 EBP: c49fbebc ESP: c49fbea0
  DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
 Process nfsiod (pid: 3646, ti=c49fa000 task=f5e3d580 task.ti=c49fa000)
 Stack:
  fc89b544 c5c790e0 f109b700 00017d78 8000082c f109b700 f10d9c00 c49fbefc
 <0> fc87cee8 00000002 00000001 00000000 c01bd123 00000046 c49fbf00 f5e3d580
 <0> f10d9d28 f10d9d30 00000000 f10d9c00 f10d9c04 f10d9c00 fc8968f8 c49fbf04
 Call Trace:
  [<fc87cee8>] ? nfs_commit_release+0x88/0x1a0 [nfs]
  [<c01bd123>] ? probe_workqueue_execution+0x33/0xa0
  [<f83ebc43>] ? rpc_release_calldata+0x13/0x20 [sunrpc]
  [<f83ebdc1>] ? rpc_free_task+0x41/0x70 [sunrpc]
  [<c015c2c6>] ? worker_thread+0x136/0x300
  [<f83ebea0>] ? rpc_async_release+0x10/0x20 [sunrpc]
  [<c015c327>] ? worker_thread+0x197/0x300
  [<c015c2c6>] ? worker_thread+0x136/0x300
  [<f83ebe90>] ? rpc_async_release+0x0/0x20 [sunrpc]
  [<c015ffb0>] ? autoremove_wake_function+0x0/0x40
  [<c015c190>] ? worker_thread+0x0/0x300
  [<c015fbd4>] ? kthread+0x74/0x80
  [<c015fb60>] ? kthread+0x0/0x80
  [<c010353a>] ? kernel_thread_helper+0x6/0x10
 Code: 0b eb fe 0f 0b eb fe 8b 03 89 44 24 10 8b 43 14 89 44 24 0c 8b 43 0c 89 5c 24 04 89 44 24 08 c7 04 24 44 b5 89 fc e8 2b 95 d2 c3 <0f> 0b eb fe 0f 0b eb fe 90 55 89 e5 57 56 53 83 ec 2c 0f 1f 44 
 EIP: [<fc87ce57>] nfs_clear_request_commit+0xf7/0x100 [nfs] SS:ESP 0068:c49fbea0
 ---[ end trace a852f1835725d3b2 ]---
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