Hello!

On Tue, Mar 08, 2011 at 03:24:47PM -0500, magz wrote:

> Hello,
>
> Is it reasonable to add following check to not clean/discard fd in case
> if it's sub request?
>
> I developed nginx module and when it started to use tmp buffers under
> load I had following error:
>
> [alert] 29663#0: *45789 sendfile() failed (9: Bad file descriptor) while
> sending request to upstream, client: 10.1.24.14, server: hss, request:
> "POST
>
> So that sub-request cleared file before main request reached it.
> Probably this bug should not appear if request body was discarded for
> sub request. But in case if you need request body for sub-request you
> should be sure that sub-request does not erases main request buffers.

In official nginx, subrequests can't appear before main
request.

On the other hand, main request may clear body as well, and it
won't be available for subrequests as a result. This problem may
be easily seen with ssi module. The other possible case when this
problem may appear is filter finalization (e.g. as done by image
filter module).

That is, just disabling body cleanup for subrequests is clearly
not enough.

I've already posted the patch which removes the code in question
at all (as a reply to some real problems seen with ssi and POSTs,
somewhere in russian mailing list). Probably it should be made
controllable via some configuration directive if there are some
real use cases which may be seriously affected by removing this
code. I would like to hear something from Igor about this.

BTW, just for history: the code in question was introduced in
nginx 0.3.3 with the following log message:

*) Bugfix: a temporary file with client request body now is removed
just after the response header was transferred to a client.

Maxim Dounin


>
>
> -- src/http/ngx_http_upstream.c_orig 2011-03-08 08:01:20.000000000
> -0800
> +++ src/http/ngx_http_upstream.c 2011-03-08 08:01:41.000000000 -0800
> @@ -2033,7 +2033,7 @@ ngx_http_upstream_send_response(ngx_http
>
> u->header_sent = 1;
>
> - if (r->request_body && r->request_body->temp_file) {
> + if (r->request_body && r->request_body->temp_file && r == r->main)
> {
> ngx_pool_run_cleanup_file(r->pool,
> r->request_body->temp_file->file.fd);
> r->request_body->temp_file->file.fd = NGX_INVALID_FILE;
> }
>
> Posted at Nginx Forum: http://forum.nginx.org/read.php?2,181400,181400#msg-181400
>
>
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