Re: [PATCH] nfs: clear_commit_release incorrectly handle truncated page

Chuck Lever
2010-02-02T20:20:52Z

On Feb 2, 2010, at 2:54 PM, Trond Myklebust wrote:
> On Tue, 2010-02-02 at 20:09 +0300, Dmitry Monakhov wrote:
>> Trond Myklebust <trond.myklebust@fys.uio.no> writes:
>>
>>> On Tue, 2010-02-02 at 19:47 +0300, Dmitry Monakhov wrote:
>>>> Trond Myklebust <trond.myklebust@fys.uio.no> writes:
>>>>> Hmm.... There is a known problem with a reference leak in
>>>>> nfs_wb_page_cancel() (I've queued up a fix for 2.6.33 in the
>>>>> 'bugfixes'
>>>>> branch of my git tree already). What happens when you apply the
>>>>> following patch?
>>>> The not helps, still get the same oops(log follows).
>>>> Have you tried my testcase?
>>>>
>>>> BUG: unable to handle kernel NULL pointer dereference at 00000040
>>>> IP: [<f80d415f>] nfs_clear_request_commit+0x3f/0xb0 [nfs]
>>>> *pde = 00000000
>>>> Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
>>>> last sysfs file: /sys/devices/platform/thinkpad_acpi/leds/
>>>> tpacpi::thinkvantage/uevent
>>>> Modules linked in: binfmt_misc quota_v2 quota_tree nfsd exportfs
>>>> nfs lockd sunrpc iwl3945 thinkpad_acpi psmouse led_class
>>>> serio_raw iwlcore nvram raid1 raid0 linear e1000e
>>>>
>>>> Pid: 1035, comm: nfsiod Not tainted 2.6.33-rc6 #60 2623DDU/2623DDU
>>>> EIP: 0060:[<f80d415f>] EFLAGS: 00010296 CPU: 0
>>>> EIP is at nfs_clear_request_commit+0x3f/0xb0 [nfs]
>>>> EAX: 00000000 EBX: c2561d80 ECX: c06d3700 EDX: 00000014
>>>> ESI: f69916c0 EDI: f80dab58 EBP: f6724ef4 ESP: f6724ee8
>>>> DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
>>>> Process nfsiod (pid: 1035, ti=f6724000 task=f69dda90
>>>> task.ti=f6724000)
>>>> Stack:
>>>> c04df67d f69d7440 f69916c0 f6724f34 f80d4258 f6724f44 00001b0e
>>>> 00000000
>>>> <0> ffff799c 00000400 f505f000 94c0042a f69917e0 f69917e8
>>>> 00000000 f69916c0
>>>> <0> f69916c4 f69916c0 f80dab58 f6724f3c f8075703 f6724f58
>>>> f8075871 f6724f60
>>>> Call Trace:
>>>> [<c04df67d>] ? schedule+0x3ad/0xa30
>>>> [<f80d4258>] ? nfs_commit_release+0x88/0x1a0 [nfs]
>>>> [<f8075703>] ? rpc_release_calldata+0x13/0x20 [sunrpc]
>>>> [<f8075871>] ? rpc_free_task+0x41/0x70 [sunrpc]
>>>> [<c01acc4c>] ? probe_workqueue_execution+0x8c/0xd0
>>>> [<f8075940>] ? rpc_async_release+0x10/0x20 [sunrpc]
>>>> [<c015834d>] ? worker_thread+0x10d/0x210
>>>> [<f8075930>] ? rpc_async_release+0x0/0x20 [sunrpc]
>>>> [<c015bb10>] ? autoremove_wake_function+0x0/0x50
>>>> [<c0158240>] ? worker_thread+0x0/0x210
>>>> [<c015b724>] ? kthread+0x74/0x80
>>>> [<c015b6b0>] ? kthread+0x0/0x80
>>>> [<c0103546>] ? kernel_thread_helper+0x6/0x10
>>>> Code: f0 0f ba 70 28 01 19 d2 31 c0 85 d2 75 0e 8b 5d f8 8b 75 fc
>>>> 89 ec 5d c3 8d 74 26 00 89 d8 ba 10 00 00 00 e8 74 0e 10 c8 8b 43
>>>> 10 <8b> 70 40 9c 5b fa e8 26 67 0d c8 8d 46 30 b9 ff ff ff ff 0f bd
>>>> EIP: [<f80d415f>] nfs_clear_request_commit+0x3f/0xb0 [nfs] SS:ESP
>>>> 0068:f6724ee8
>>>> CR2: 0000000000000040
>>>> ---[ end trace 4bf8ee9d233ce744 ]---
>>>
>>> Yep. Looking more carefully at your test case, I don't see how
>>> truncate_inode_page() can be involved at all. You are extending
>>> the file
>>> using lseek(), not truncate(). So something else must be at work
>>> here.
>> open(,O_TRUNC,)
>> do_filp_open()
>> handle_truncate()
>> do_truncate()
>> Yess this is craziness to run concurrent tasks which do:
>> open(,O_TRUNC,); mmap();
>> But initially i've done this by occasion and this result in OOps :)
>>>
>>> I'll see if I can reproduce it.
>>>
>
> OK. I haven't been able to reproduce your bug yet, but I think I see
> what is happening.
>
> Your 'kill -9' will occasionally hit nfs_wb_page_cancel() and cause it
> to fail. When _that_ happens, then all hell breaks loose, because
> mapping->a_ops->invalidatepage() is not allowed to fail.
>
> Ugh... I don't think there much of an alternative to making
> nfs_wait_on_request() uninterruptible. On the plus side, that does
> make
> the behaviour of the NFS writeback code consistent with that of the
> VFS
> layer (i.e. wait_on_page_writeback()).
>
> So here goes...
>
> Trond
> ----------------------------------------------------------------------------------------------
> NFS: Fix an Oops when truncating a file
>
> From: Trond Myklebust <Trond.Myklebust@netapp.com>
>
> The VM/VFS does not allow mapping->a_ops->invalidatepage() to fail.
> Unfortunately, nfs_wb_page_cancel() may fail if a fatal signal occurs.
> Since the NFS code assumes that the page stays mapped for as long as
> the
> writeback is active, we can end up Oopsing (among other things).
>
> The only safe fix here is to convert nfs_wait_on_request(), so as to
> make
> it uninterruptible (as is already the case with
> wait_on_page_writeback()).

What happens when the server is unreachable while we're in
nfs_wait_on_request?

> Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
> ---
>
> fs/nfs/pagelist.c | 17 +++++++++--------
> 1 files changed, 9 insertions(+), 8 deletions(-)
>
>
> diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
> index e297593..a12c45b 100644
> --- a/fs/nfs/pagelist.c
> +++ b/fs/nfs/pagelist.c
> @@ -176,6 +176,12 @@ void nfs_release_request(struct nfs_page *req)
> kref_put(&req->wb_kref, nfs_free_request);
> }
>
> +static int nfs_wait_bit_uninterruptible(void *word)
> +{
> + io_schedule();
> + return 0;
> +}
> +
> /**
> * nfs_wait_on_request - Wait for a request to complete.
> * @req: request to wait upon.
> @@ -186,14 +192,9 @@ void nfs_release_request(struct nfs_page *req)
> int
> nfs_wait_on_request(struct nfs_page *req)
> {
> - int ret = 0;
> -
> - if (!test_bit(PG_BUSY, &req->wb_flags))
> - goto out;
> - ret = out_of_line_wait_on_bit(&req->wb_flags, PG_BUSY,
> - nfs_wait_bit_killable, TASK_KILLABLE);
> -out:
> - return ret;
> + return wait_on_bit(&req->wb_flags, PG_BUSY,
> + nfs_wait_bit_uninterruptible,
> + TASK_UNINTERRUPTIBLE);
> }
>
> /**
>
>
> --
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--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com