Nginx eats 100% cpu in ngx_event_pipe_write_to_downstream

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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