Nginx eats 100% cpu in ngx_event_pipe_write_to_downstream

[Breno Silva]

Hello list,

We are porting ModSecurity to NGINX. However we are seeing sometimes an
issue. Nginx eats 100% of cpu and when i use gdb i see:

gdb -p 8645

ngx_event_pipe_write_to_downstream (p=0x9bbc720, do_write=0) at
src/event/ngx_event_pipe.c:551

551 if (cl->buf->recycled) {
(gdb)

Looks like it is happening when we call ngx_http_modsecurity_body_filter()
then go to this conditions;

    rc = move_chain_to_brigade(in, ctx->brigade, r->pool, 0);

    if (rc != NGX_OK)  {

        r->buffered |= NGX_HTTP_SSI_BUFFERED;

        return rc;

     }

move_chainto_brigade is defined as:


ngx_int_t

move_chain_to_brigade(ngx_chain_t *chain, apr_bucket_brigade *bb,
ngx_pool_t *pool, ngx_int_t last_buf) {

    apr_bucket         *e;

    ngx_chain_t        *cl;


    while (chain) {

        e = ngx_buf_to_apr_bucket(chain->buf, bb->p, bb->bucket_alloc);

        if (e == NULL) {

            return NGX_ERROR;

        }


        APR_BRIGADE_INSERT_TAIL(bb, e);

        if (chain->buf->last_buf) {

            e = apr_bucket_eos_create(bb->bucket_alloc);

            APR_BRIGADE_INSERT_TAIL(bb, e);

            chain->buf->last_buf = 0;

            return NGX_OK;

        }

        cl = chain;

        chain = chain->next;

        ngx_free_chain(pool, cl);

    }


    if (last_buf) {

        e = apr_bucket_eos_create(bb->bucket_alloc);

        APR_BRIGADE_INSERT_TAIL(bb, e);

        return NGX_OK;

    }

    return NGX_AGAIN;

}
Let me know if you guys can help us understanding why sometimes we trigger
this issue
Thanks

Breno
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