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view src/http/ngx_http_write_filter_module.c @ 7975:a7a77549265e

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HTTP/2: fixed sendfile() aio handling. With sendfile() in threads ("aio threads; sendfile on;"), client connection can block on writing, waiting for sendfile() to complete. In HTTP/2 this might result in the request hang, since an attempt to continue processing in thread event handler will call request's write event handler, which is usually stopped by ngx_http_v2_send_chain(): it does nothing if there are no additional data and stream->queued is set. Further, HTTP/2 resets stream's c->write->ready to 0 if writing blocks, so just fixing ngx_http_v2_send_chain() is not enough. Can be reproduced with test suite on Linux with: TEST_NGINX_GLOBALS_HTTP="aio threads; sendfile on;" prove h2*.t The following tests currently fail: h2_keepalive.t, h2_priority.t, h2_proxy_max_temp_file_size.t, h2.t, h2_trailers.t. Similarly, sendfile() with AIO preloading on FreeBSD can block as well, with similar results. This is, however, harder to reproduce, especially on modern FreeBSD systems, since sendfile() usually does not return EBUSY. Fix is to modify ngx_http_v2_send_chain() so it actually tries to send data to the main connection when called, and to make sure that c->write->ready is set by the relevant event handlers.
author Maxim Dounin <mdounin@mdounin.ru>
date Thu, 25 Nov 2021 22:02:10 +0300
parents 51a260276425
children 32b0ba4855a6 61d0fa67b55e
line wrap: on
line source


/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>


static ngx_int_t ngx_http_write_filter_init(ngx_conf_t *cf);


static ngx_http_module_t  ngx_http_write_filter_module_ctx = {
    NULL,                                  /* preconfiguration */
    ngx_http_write_filter_init,            /* postconfiguration */

    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

    NULL,                                  /* create server configuration */
    NULL,                                  /* merge server configuration */

    NULL,                                  /* create location configuration */
    NULL,                                  /* merge location configuration */
};


ngx_module_t  ngx_http_write_filter_module = {
    NGX_MODULE_V1,
    &ngx_http_write_filter_module_ctx,     /* module context */
    NULL,                                  /* module directives */
    NGX_HTTP_MODULE,                       /* module type */
    NULL,                                  /* init master */
    NULL,                                  /* init module */
    NULL,                                  /* init process */
    NULL,                                  /* init thread */
    NULL,                                  /* exit thread */
    NULL,                                  /* exit process */
    NULL,                                  /* exit master */
    NGX_MODULE_V1_PADDING
};


ngx_int_t
ngx_http_write_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
    off_t                      size, sent, nsent, limit;
    ngx_uint_t                 last, flush, sync;
    ngx_msec_t                 delay;
    ngx_chain_t               *cl, *ln, **ll, *chain;
    ngx_connection_t          *c;
    ngx_http_core_loc_conf_t  *clcf;

    c = r->connection;

    if (c->error) {
        return NGX_ERROR;
    }

    size = 0;
    flush = 0;
    sync = 0;
    last = 0;
    ll = &r->out;

    /* find the size, the flush point and the last link of the saved chain */

    for (cl = r->out; cl; cl = cl->next) {
        ll = &cl->next;

        ngx_log_debug7(NGX_LOG_DEBUG_EVENT, c->log, 0,
                       "write old buf t:%d f:%d %p, pos %p, size: %z "
                       "file: %O, size: %O",
                       cl->buf->temporary, cl->buf->in_file,
                       cl->buf->start, cl->buf->pos,
                       cl->buf->last - cl->buf->pos,
                       cl->buf->file_pos,
                       cl->buf->file_last - cl->buf->file_pos);

        if (ngx_buf_size(cl->buf) == 0 && !ngx_buf_special(cl->buf)) {
            ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                          "zero size buf in writer "
                          "t:%d r:%d f:%d %p %p-%p %p %O-%O",
                          cl->buf->temporary,
                          cl->buf->recycled,
                          cl->buf->in_file,
                          cl->buf->start,
                          cl->buf->pos,
                          cl->buf->last,
                          cl->buf->file,
                          cl->buf->file_pos,
                          cl->buf->file_last);

            ngx_debug_point();
            return NGX_ERROR;
        }

        if (ngx_buf_size(cl->buf) < 0) {
            ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                          "negative size buf in writer "
                          "t:%d r:%d f:%d %p %p-%p %p %O-%O",
                          cl->buf->temporary,
                          cl->buf->recycled,
                          cl->buf->in_file,
                          cl->buf->start,
                          cl->buf->pos,
                          cl->buf->last,
                          cl->buf->file,
                          cl->buf->file_pos,
                          cl->buf->file_last);

            ngx_debug_point();
            return NGX_ERROR;
        }

        size += ngx_buf_size(cl->buf);

        if (cl->buf->flush || cl->buf->recycled) {
            flush = 1;
        }

        if (cl->buf->sync) {
            sync = 1;
        }

        if (cl->buf->last_buf) {
            last = 1;
        }
    }

    /* add the new chain to the existent one */

    for (ln = in; ln; ln = ln->next) {
        cl = ngx_alloc_chain_link(r->pool);
        if (cl == NULL) {
            return NGX_ERROR;
        }

        cl->buf = ln->buf;
        *ll = cl;
        ll = &cl->next;

        ngx_log_debug7(NGX_LOG_DEBUG_EVENT, c->log, 0,
                       "write new buf t:%d f:%d %p, pos %p, size: %z "
                       "file: %O, size: %O",
                       cl->buf->temporary, cl->buf->in_file,
                       cl->buf->start, cl->buf->pos,
                       cl->buf->last - cl->buf->pos,
                       cl->buf->file_pos,
                       cl->buf->file_last - cl->buf->file_pos);

        if (ngx_buf_size(cl->buf) == 0 && !ngx_buf_special(cl->buf)) {
            ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                          "zero size buf in writer "
                          "t:%d r:%d f:%d %p %p-%p %p %O-%O",
                          cl->buf->temporary,
                          cl->buf->recycled,
                          cl->buf->in_file,
                          cl->buf->start,
                          cl->buf->pos,
                          cl->buf->last,
                          cl->buf->file,
                          cl->buf->file_pos,
                          cl->buf->file_last);

            ngx_debug_point();
            return NGX_ERROR;
        }

        if (ngx_buf_size(cl->buf) < 0) {
            ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                          "negative size buf in writer "
                          "t:%d r:%d f:%d %p %p-%p %p %O-%O",
                          cl->buf->temporary,
                          cl->buf->recycled,
                          cl->buf->in_file,
                          cl->buf->start,
                          cl->buf->pos,
                          cl->buf->last,
                          cl->buf->file,
                          cl->buf->file_pos,
                          cl->buf->file_last);

            ngx_debug_point();
            return NGX_ERROR;
        }

        size += ngx_buf_size(cl->buf);

        if (cl->buf->flush || cl->buf->recycled) {
            flush = 1;
        }

        if (cl->buf->sync) {
            sync = 1;
        }

        if (cl->buf->last_buf) {
            last = 1;
        }
    }

    *ll = NULL;

    ngx_log_debug3(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "http write filter: l:%ui f:%ui s:%O", last, flush, size);

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    /*
     * avoid the output if there are no last buf, no flush point,
     * there are the incoming bufs and the size of all bufs
     * is smaller than "postpone_output" directive
     */

    if (!last && !flush && in && size < (off_t) clcf->postpone_output) {
        return NGX_OK;
    }

    if (c->write->delayed) {
        c->buffered |= NGX_HTTP_WRITE_BUFFERED;
        return NGX_AGAIN;
    }

    if (size == 0
        && !(c->buffered & NGX_LOWLEVEL_BUFFERED)
        && !(last && c->need_last_buf))
    {
        if (last || flush || sync) {
            for (cl = r->out; cl; /* void */) {
                ln = cl;
                cl = cl->next;
                ngx_free_chain(r->pool, ln);
            }

            r->out = NULL;
            c->buffered &= ~NGX_HTTP_WRITE_BUFFERED;

            return NGX_OK;
        }

        ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                      "the http output chain is empty");

        ngx_debug_point();

        return NGX_ERROR;
    }

    if (!r->limit_rate_set) {
        r->limit_rate = ngx_http_complex_value_size(r, clcf->limit_rate, 0);
        r->limit_rate_set = 1;
    }

    if (r->limit_rate) {

        if (!r->limit_rate_after_set) {
            r->limit_rate_after = ngx_http_complex_value_size(r,
                                                    clcf->limit_rate_after, 0);
            r->limit_rate_after_set = 1;
        }

        limit = (off_t) r->limit_rate * (ngx_time() - r->start_sec + 1)
                - (c->sent - r->limit_rate_after);

        if (limit <= 0) {
            c->write->delayed = 1;
            delay = (ngx_msec_t) (- limit * 1000 / r->limit_rate + 1);
            ngx_add_timer(c->write, delay);

            c->buffered |= NGX_HTTP_WRITE_BUFFERED;

            return NGX_AGAIN;
        }

        if (clcf->sendfile_max_chunk
            && (off_t) clcf->sendfile_max_chunk < limit)
        {
            limit = clcf->sendfile_max_chunk;
        }

    } else {
        limit = clcf->sendfile_max_chunk;
    }

    sent = c->sent;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "http write filter limit %O", limit);

    chain = c->send_chain(c, r->out, limit);

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "http write filter %p", chain);

    if (chain == NGX_CHAIN_ERROR) {
        c->error = 1;
        return NGX_ERROR;
    }

    if (r->limit_rate) {

        nsent = c->sent;

        if (r->limit_rate_after) {

            sent -= r->limit_rate_after;
            if (sent < 0) {
                sent = 0;
            }

            nsent -= r->limit_rate_after;
            if (nsent < 0) {
                nsent = 0;
            }
        }

        delay = (ngx_msec_t) ((nsent - sent) * 1000 / r->limit_rate);

        if (delay > 0) {
            c->write->delayed = 1;
            ngx_add_timer(c->write, delay);
        }
    }

    if (chain && c->write->ready && !c->write->delayed) {
        ngx_post_event(c->write, &ngx_posted_next_events);
    }

    for (cl = r->out; cl && cl != chain; /* void */) {
        ln = cl;
        cl = cl->next;
        ngx_free_chain(r->pool, ln);
    }

    r->out = chain;

    if (chain) {
        c->buffered |= NGX_HTTP_WRITE_BUFFERED;
        return NGX_AGAIN;
    }

    c->buffered &= ~NGX_HTTP_WRITE_BUFFERED;

    if ((c->buffered & NGX_LOWLEVEL_BUFFERED) && r->postponed == NULL) {
        return NGX_AGAIN;
    }

    return NGX_OK;
}


static ngx_int_t
ngx_http_write_filter_init(ngx_conf_t *cf)
{
    ngx_http_top_body_filter = ngx_http_write_filter;

    return NGX_OK;
}