Fixed request termination with AIO and subrequests (ticket #2555). When a request was terminated due to an error via ngx_http_terminate_request() while an AIO operation was running in a subrequest, various issues were observed. This happened because ngx_http_request_finalizer() was only set in the subrequest where ngx_http_terminate_request() was called, but not in the subrequest where the AIO operation was running. After completion of the AIO operation normal processing of the subrequest was resumed, leading to issues. In particular, in case of the upstream module, termination of the request called upstream cleanup, which closed the upstream connection. Attempts to further work with the upstream connection after AIO operation completion resulted in segfaults in ngx_ssl_recv(), "readv() failed (9: Bad file descriptor) while reading upstream" errors, or socket leaks. In ticket #2555, issues were observed with the following configuration with cache background update (with thread writing instrumented to introduce a delay, when a client closes the connection during an update): location = /background-and-aio-write { proxy_pass ... proxy_cache one; proxy_cache_valid 200 1s; proxy_cache_background_update on; proxy_cache_use_stale updating; aio threads; aio_write on; limit_rate 1000; } Similarly, the same issue can be seen with SSI, and can be caused by errors in subrequests, such as in the following configuration (where "/proxy" uses AIO, and "/sleep" returns 444 after some delay, causing request termination): location = /ssi-active-boom { ssi on; ssi_types *; return 200 ' <!--#include virtual="/proxy" --> <!--#include virtual="/sleep" --> '; limit_rate 1000; } Or the same with both AIO operation and the error in non-active subrequests (which needs slightly different handling, see below): location = /ssi-non-active-boom { ssi on; ssi_types *; return 200 ' <!--#include virtual="/static" --> <!--#include virtual="/proxy" --> <!--#include virtual="/sleep" --> '; limit_rate 1000; } Similarly, issues can be observed with just static files. However, with static files potential impact is limited due to timeout safeguards in ngx_http_writer(), and the fact that c->error is set during request termination. In a simple configuration with an AIO operation in the active subrequest, such as in the following configuration, the connection is closed right after completion of the AIO operation anyway, since ngx_http_writer() tries to write to the connection and fails due to c->error set: location = /ssi-active-static-boom { ssi on; ssi_types *; return 200 ' <!--#include virtual="/static-aio" --> <!--#include virtual="/sleep" --> '; limit_rate 1000; } In the following configuration, with an AIO operation in a non-active subrequest, the connection is closed only after send_timeout expires: location = /ssi-non-active-static-boom { ssi on; ssi_types *; return 200 ' <!--#include virtual="/static" --> <!--#include virtual="/static-aio" --> <!--#include virtual="/sleep" --> '; limit_rate 1000; } Fix is to introduce r->main->terminated flag, which is to be checked by AIO event handlers when the r->main->blocked counter is decremented. When the flag is set, handlers are expected to wake up the connection instead of the subrequest (which might be already cleaned up). Additionally, now ngx_http_request_finalizer() is always set in the active subrequest, so waking up the connection properly finalizes the request even if termination happened in a non-active subrequest.

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


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

#define NGX_BPF_LOGBUF_SIZE  (16 * 1024)


static ngx_inline int
ngx_bpf(enum bpf_cmd cmd, union bpf_attr *attr, unsigned int size)
{
    return syscall(__NR_bpf, cmd, attr, size);
}


void
ngx_bpf_program_link(ngx_bpf_program_t *program, const char *symbol, int fd)
{
    ngx_uint_t        i;
    ngx_bpf_reloc_t  *rl;

    rl = program->relocs;

    for (i = 0; i < program->nrelocs; i++) {
        if (ngx_strcmp(rl[i].name, symbol) == 0) {
            program->ins[rl[i].offset].src_reg = 1;
            program->ins[rl[i].offset].imm = fd;
        }
    }
}


int
ngx_bpf_load_program(ngx_log_t *log, ngx_bpf_program_t *program)
{
    int             fd;
    union bpf_attr  attr;
#if (NGX_DEBUG)
    char            buf[NGX_BPF_LOGBUF_SIZE];
#endif

    ngx_memzero(&attr, sizeof(union bpf_attr));

    attr.license = (uintptr_t) program->license;
    attr.prog_type = program->type;
    attr.insns = (uintptr_t) program->ins;
    attr.insn_cnt = program->nins;

#if (NGX_DEBUG)
    /* for verifier errors */
    attr.log_buf = (uintptr_t) buf;
    attr.log_size = NGX_BPF_LOGBUF_SIZE;
    attr.log_level = 1;
#endif

    fd = ngx_bpf(BPF_PROG_LOAD, &attr, sizeof(attr));
    if (fd < 0) {
        ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,
                      "failed to load BPF program");

        ngx_log_debug1(NGX_LOG_DEBUG_CORE, log, 0,
                       "bpf verifier: %s", buf);

        return -1;
    }

    return fd;
}


int
ngx_bpf_map_create(ngx_log_t *log, enum bpf_map_type type, int key_size,
    int value_size, int max_entries, uint32_t map_flags)
{
    int             fd;
    union bpf_attr  attr;

    ngx_memzero(&attr, sizeof(union bpf_attr));

    attr.map_type = type;
    attr.key_size = key_size;
    attr.value_size = value_size;
    attr.max_entries = max_entries;
    attr.map_flags = map_flags;

    fd = ngx_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
    if (fd < 0) {
        ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,
                      "failed to create BPF map");
        return NGX_ERROR;
    }

    return fd;
}


int
ngx_bpf_map_update(int fd, const void *key, const void *value, uint64_t flags)
{
    union bpf_attr attr;

    ngx_memzero(&attr, sizeof(union bpf_attr));

    attr.map_fd = fd;
    attr.key = (uintptr_t) key;
    attr.value = (uintptr_t) value;
    attr.flags = flags;

    return ngx_bpf(BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr));
}


int
ngx_bpf_map_delete(int fd, const void *key)
{
    union bpf_attr attr;

    ngx_memzero(&attr, sizeof(union bpf_attr));

    attr.map_fd = fd;
    attr.key = (uintptr_t) key;

    return ngx_bpf(BPF_MAP_DELETE_ELEM, &attr, sizeof(attr));
}


int
ngx_bpf_map_lookup(int fd, const void *key, void *value)
{
    union bpf_attr attr;

    ngx_memzero(&attr, sizeof(union bpf_attr));

    attr.map_fd = fd;
    attr.key = (uintptr_t) key;
    attr.value = (uintptr_t) value;

    return ngx_bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));
}