Re: [PATCH] Clear fd after closing to avoid double-close error

From: Jens Lindström <jl@opera.com>
Date: Oct 22, 2013, 13:15 UTC
Message-ID: <CAEef6Wx7K0KJK-dMJ2HTgdoGvVhve7=rHK8gv1gQc7GO5_K0WA@mail.gmail.com>
In-Reply-To: <CACsJy8DtvaojrrQr4=uYCRse7N+SXb+WdjY+C_0FRSjYsNC6zg@mail.gmail.com>

On Tue, Oct 22, 2013 at 2:39 PM, Duy Nguyen <pclouds@gmail.com> wrote:

> Not your itch. But if you have time you may want to fix fetch-pack
> too. It has the same problem. fetch-pack.c:get_pack() with
> use_sideband == 0 passes fd[0] to start_command(), then later its
> caller transport.c:fetch_refs_via_pack() closes the handle again.

I'll update the patch to clear that fd as well.

Show 14 quoted lines

>> Signed-off-by: Jens Lindström <jl@opera.com>
>> ---
>>  send-pack.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/send-pack.c b/send-pack.c
>> index 7d172ef..7def2af 100644
>> --- a/send-pack.c
>> +++ b/send-pack.c
>> @@ -302,6 +302,9 @@ int send_pack(struct send_pack_args *args,
>>                                 finish_async(&demux);
>>                         return -1;
>
> In this code block, there is "close(out);", we may need to set fd[1] = -1 too.

This block closes the fd unconditionally, I think. Either via pack_objects() (if !args->stateless_rpc) or directly (otherwise.) So I guess it should always clear the fd before returning to be safe.

Show 16 quoted lines

>>                 }
>> +               if (!args->stateless_rpc)
>> +                       /* Closed by pack_objects() via start_command() */
>> +                       fd[1] = -1;
>>         }
>>         if (args->stateless_rpc && cmds_sent)
>>                 packet_flush(out);
>
> I was puzzled by this packet_flush(out) for a while because I thought
> "out" was already closed. Turns out when stateless_rpc is true, a new
> pipe is created in pack_objects() and "out" is not closed. So
> everything is still good (and messy).
>
> Life would have been simpler if fd[1] was _always_ closed by
> send_pack(), like in c20181e (start_command(), if .in/.out > 0, closes
> file descriptors, not the callers - 2008-02-21).

It did strike me as a bit unclear who exactly "owned" these file descriptors. But I'm of course wholly unfamiliar with this code.

/ Jens