[PATCH 2 of 4] Fix of cpu hog in event pipe

[Maxim Dounin]

# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1316368093 -14400
# Node ID e71db1db1a002ef34d6f6b24cd1c2059f8df58f5
# Parent  187de3097048531a3bd3d7a84a40657d1f0df216
Fix of cpu hog in event pipe.

If client closed connection in ngx_event_pipe_write_to_downstream(), buffers
in the "out" chain were lost.  This caused cpu hog if all available buffers
were in the "out" chain.  Fix is to call ngx_chain_update_chains() before
checking return code of output filter to avoid loosing buffers in the "out"
chain.

Note that this situation (all available buffers in the "out" chain) isn't
normal, it should be prevented by busy buffers limit.  Though right now it
may happen with complex protocols like fastcgi.  This should be addressed
separately.

diff --git a/src/event/ngx_event_pipe.c b/src/event/ngx_event_pipe.c
--- a/src/event/ngx_event_pipe.c
+++ b/src/event/ngx_event_pipe.c
@@ -656,13 +656,13 @@ ngx_event_pipe_write_to_downstream(ngx_e
 
         rc = p->output_filter(p->output_ctx, out);
 
+        ngx_chain_update_chains(p->pool, &p->free, &p->busy, &out, p->tag);
+
         if (rc == NGX_ERROR) {
             p->downstream_error = 1;
             return ngx_event_pipe_drain_chains(p);
         }
 
-        ngx_chain_update_chains(p->pool, &p->free, &p->busy, &out, p->tag);
-
         for (cl = p->free; cl; cl = cl->next) {
 
             if (cl->buf->temp_file) {