Upstream: fixed proxy_no_cache when caching errors. Caching errors, notably intercepted errors and internally generated 502/504 errors, as well as handling of cache revalidation with 304, did not take into account u->conf->no_cache predicates configured. As a result, an error might be cached even if configuration explicitly says not to. Fix is to check u->conf->no_cache in these cases. To simplify usage in multiple places, checking u->conf->no_cache is now done in a separate function. As a minor optimization, u->conf->no_cache is only checked if u->cacheable is set. As a side effect, this change also fixes caching errors after proxy_cache_bypass. Also, during cache revalidation u->cacheable is now tested, so 304 responses which disable caching won't extend cacheability of stored responses. Additionally, when caching internally generated 502/504 errors u->cacheable is now explicitly updated from u->headers_in.no_cache and u->headers_in.expired, restoring the behaviour before 8041:0784ab86ad08 (1.23.0) when an error happens while reading the response headers. Reported by Kirill A. Korinsky, https://freenginx.org/pipermail/nginx/2024-April/000082.html

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


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


void
ngx_spinlock(ngx_atomic_t *lock, ngx_atomic_int_t value, ngx_uint_t spin)
{

#if (NGX_HAVE_ATOMIC_OPS)

    ngx_uint_t  i, n;

    for ( ;; ) {

        if (*lock == 0 && ngx_atomic_cmp_set(lock, 0, value)) {
            return;
        }

        if (ngx_ncpu > 1) {

            for (n = 1; n < spin; n <<= 1) {

                for (i = 0; i < n; i++) {
                    ngx_cpu_pause();
                }

                if (*lock == 0 && ngx_atomic_cmp_set(lock, 0, value)) {
                    return;
                }
            }
        }

        ngx_sched_yield();
    }

#else

#if (NGX_THREADS)

#error ngx_spinlock() or ngx_atomic_cmp_set() are not defined !

#endif

#endif

}