Re: [Xen-devel] [Xen-users] "xl restore" leaks a file descriptor?

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/08/15 16:48, Ian Campbell wrote:
> On Tue, 2015-08-11 at 11:13 -0400, Andrew Armenia wrote:
>> It's the checkpoint file - i.e. the command line argument to xl
>> restore - that is being leaked.
> Thanks.
>
> [...]
>> So the checkpoint file is clearly being leaked.
> Indeed. I confirmed this even with the current development version using ls
> -l /proc/<pid>/fd which shows an fd open on a deleted file:
>
> # ps aux| grep xl
> root     20465  0.0  0.2 106036   984 ?        SLsl 15:42   0:00 xl restore 
> save
> # ls -l /proc/20465/fd
> [...]
> lr-x------. 1 root root 64 Aug 11 15:42 7 -> /root/save
> [...]
> # rm /root/save
> # ls -l /proc/20465/fd
> [...]
> lr-x------. 1 root root 64 Aug 11 15:42 7 -> /root/save (deleted)
> [...]
>
>>  Its space is not freed
>> until the 'xl restore' process is ended by shutting down the domain:
> [...]
>> It seems like xl restore should close the checkpoint file as soon as
>> it's done restoring the domain, allowing the space to be freed, but
>> that's clearly not happening.
> Right. In fact xl sets the file to be close-on-exec right after opening it,
> which is before the daemonisation step, so it ought to be closed
> automatically, but isn't for some reason.
>
> My working theory is that something in the machinery which spawns the save
> helper is defeating the use of CLOEXEC, perhaps by dup2() or perhaps by
> unsetting CLOEXEC.
>
> Any way, thanks for reporting. I've copied the devel list and 4.6 RM. Wei
> this probably ought to be a blocker for 4.6 (and the fix ought ultimately
> to be backported to 4.4 onwards at least).
>
> NB: This leak seems to be independent of the switch to migration v2.

IIRC, the file descriptor for this is fcntl()'d by at least 3 separate
bits of code (libxl, libxl-save-helper, libxc) once it has been passed
into libxl.

I would not be surprised if one of the higher levels accidentally
clobbered CLOEXEC.

~Andrew

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