[Buildroot] [PATCH] package/nginx: fix NGINX pidfile handling systemd

[Yann E. MORIN <yann.morin.1998@free.fr>]

Matthew, All,

On 2021-05-21 09:41 -0500, Matthew Weber via buildroot spake thusly:
> Based on https://git.launchpad.net/ubuntu/+source/nginx/plain/debian/patches/nginx-fix-pidfile.patch
> Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/nginx/+bug/1581864
> Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876365
> 
> Upstream bug: (deferred fix)
> https://trac.nginx.org/nginx/ticket/1897?cversion=0&cnum_hist=2

So, basically, upstream refused to fix that bug, because (re-ordered so
that what I believe most important gets listed first):

  - the believe the Ubuntu patch (which this is based on) is incorrect:
    "The patch suggested in the Ubuntu bugtracker to write pidfile in
    the parent process looks wrong. In particular, it does so with the
    wrong umask, which is set in the child process only."

  - they believe the synchronisation described in systemd's doc is too
    complex:
    "The patch to synchronize things as recommended bysystemd's
    daemon(7) manpage [...] wasn't committed as the change is considered
    too complex for the problem it solves"

  - they believe the message is innocuous (I suppose because systemd
    will loop to TERM then KILL all proceses in a cgroup, thus actually
    and eventually ending the nginx daemon).

  - a then-future version of systemd should include support for that
    situation with new the new unit directive "Type=pid-file"

 - a few various lesser interesting (to us) reasons

However, there seems to be an easy workaround: complement the systemd
unit with:

    ExecStartPost=/bin/sleep 0.1

(or even a bigger number if we want to support slow systems).

Given that the patch on the code was rejected by upstream, I am wary to
bundle it in Buildroot, because we will supposedly have to carry it
forever. In this respect, tweaking the ystemd unit seems a leser burden.

However, what about the systemd situation: is the reference
Type=pid-file feautre now implemented? Do we have it in the version
packaged in Buildroot?

If so, maybe we could then tweak the unit to make use of it, instead of
the sleep workaround?

Regards,
Yann E. MORIN.

> Signed-off-by: Matthew Weber <matthew.weber@collins.com>
> ---
>  .../0010-Fix-NGINX-pidfile-handling.patch     | 105 ++++++++++++++++++
>  1 file changed, 105 insertions(+)
>  create mode 100644 package/nginx/0010-Fix-NGINX-pidfile-handling.patch
> 
> diff --git a/package/nginx/0010-Fix-NGINX-pidfile-handling.patch b/package/nginx/0010-Fix-NGINX-pidfile-handling.patch
> new file mode 100644
> index 0000000000..9a50118434
> --- /dev/null
> +++ b/package/nginx/0010-Fix-NGINX-pidfile-handling.patch
> @@ -0,0 +1,105 @@
> +From 2491379370059c7b9a2b956a49c90a9de55f5dcb Mon Sep 17 00:00:00 2001
> +From: Tj <ubuntu@iam.tj>
> +Date: Fri, 21 May 2021 09:35:53 -0500
> +Subject: [PATCH] Fix NGINX pidfile handling
> +
> +Based on https://git.launchpad.net/ubuntu/+source/nginx/plain/debian/patches/nginx-fix-pidfile.patch
> +Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/nginx/+bug/1581864
> +Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876365
> +Last-Update: 2020-06-24
> +
> +Upstream bug: (deferred fix)
> +https://trac.nginx.org/nginx/ticket/1897?cversion=0&cnum_hist=2
> +
> +Signed-off-by: Tj <ubuntu@iam.tj>
> +Signed-off-by: Matthew Weber <matthew.weber@collins.com>
> +---
> + src/core/nginx.c         | 24 +++++++++++++++++++++---
> + src/os/unix/ngx_daemon.c |  8 ++++++--
> + 2 files changed, 27 insertions(+), 5 deletions(-)
> +
> +diff --git a/src/core/nginx.c b/src/core/nginx.c
> +index 9fcb0eb..083eba1 100644
> +--- a/src/core/nginx.c
> ++++ b/src/core/nginx.c
> +@@ -338,14 +338,21 @@ main(int argc, char *const *argv)
> +         ngx_process = NGX_PROCESS_MASTER;
> +     }
> + 
> ++    /* tell-tale to detect if this is parent or child process */
> ++    ngx_int_t child_pid = NGX_BUSY;
> ++
> + #if !(NGX_WIN32)
> + 
> +     if (ngx_init_signals(cycle->log) != NGX_OK) {
> +         return 1;
> +     }
> + 
> ++    /* tell-tale that this code has been executed */
> ++    child_pid--;
> ++
> +     if (!ngx_inherited && ccf->daemon) {
> +-        if (ngx_daemon(cycle->log) != NGX_OK) {
> ++        child_pid = ngx_daemon(cycle->log);
> ++        if (child_pid == NGX_ERROR) {
> +             return 1;
> +         }
> + 
> +@@ -358,8 +365,19 @@ main(int argc, char *const *argv)
> + 
> + #endif
> + 
> +-    if (ngx_create_pidfile(&ccf->pid, cycle->log) != NGX_OK) {
> +-        return 1;
> ++    /* If ngx_daemon() returned the child's PID in the parent process
> ++     * after the fork() set ngx_pid to the child_pid, which gets
> ++     * written to the PID file, then exit.
> ++     * For NGX_WIN32 always write the PID file
> ++     * For others, only write it from the parent process */
> ++    if (child_pid < NGX_OK || child_pid > NGX_OK) {
> ++	ngx_pid = child_pid > NGX_OK ? child_pid : ngx_pid;
> ++        if (ngx_create_pidfile(&ccf->pid, cycle->log) != NGX_OK) {
> ++            return 1;
> ++	}
> ++    }
> ++    if (child_pid > NGX_OK) {
> ++        exit(0);
> +     }
> + 
> +     if (ngx_log_redirect_stderr(cycle) != NGX_OK) {
> +diff --git a/src/os/unix/ngx_daemon.c b/src/os/unix/ngx_daemon.c
> +index 385c49b..3719854 100644
> +--- a/src/os/unix/ngx_daemon.c
> ++++ b/src/os/unix/ngx_daemon.c
> +@@ -7,14 +7,17 @@
> + 
> + #include <ngx_config.h>
> + #include <ngx_core.h>
> ++#include <unistd.h>
> + 
> + 
> + ngx_int_t
> + ngx_daemon(ngx_log_t *log)
> + {
> +     int  fd;
> ++    /* retain the return value for passing back to caller */
> ++    pid_t pid_child = fork();
> + 
> +-    switch (fork()) {
> ++    switch (pid_child) {
> +     case -1:
> +         ngx_log_error(NGX_LOG_EMERG, log, ngx_errno, "fork() failed");
> +         return NGX_ERROR;
> +@@ -23,7 +26,8 @@ ngx_daemon(ngx_log_t *log)
> +         break;
> + 
> +     default:
> +-        exit(0);
> ++        /* let caller do the exit() */
> ++        return pid_child;
> +     }
> + 
> +     ngx_parent = ngx_pid;
> +-- 
> +2.17.1
> +
> -- 
> 2.17.1
> 
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