MEDIUM: shctx: Naming shared memory context

From Linux 5.17, anonymous regions can be name via prctl/PR_SET_VMA
so caches can be identified when looking at HAProxy process memory
mapping.
The most possible error is lack of kernel support, as a result
we ignore it, if the naming fails the mapping of memory context
ought to still occur.

include/haproxy/shctx.h

@@ -21,7 +21,7 @@
 
 int shctx_init(struct shared_context **orig_shctx,
                int maxblocks, int blocksize, unsigned int maxobjsz,
-               int extra);
+               int extra, __maybe_unused const char *name);
 struct shared_block *shctx_row_reserve_hot(struct shared_context *shctx,
                                            struct shared_block *last, int data_len);
 void shctx_row_detach(struct shared_context *shctx, struct shared_block *first);

src/cache.c

@@ -2471,7 +2471,7 @@ int post_check_cache()
 	list_for_each_entry_safe(cache_config, back, &caches_config, list) {
 
 		ret_shctx = shctx_init(&shctx, cache_config->maxblocks, CACHE_BLOCKSIZE,
-		                       cache_config->maxobjsz, sizeof(struct cache));
+		                       cache_config->maxobjsz, sizeof(struct cache), cache_config->id);
 
 		if (ret_shctx <= 0) {
 			if (ret_shctx == SHCTX_E_INIT_LOCK)

src/shctx.c

@@ -16,6 +16,9 @@
 #include <import/ebmbtree.h>
 #include <haproxy/list.h>
 #include <haproxy/shctx.h>
+#if defined(USE_PRCTL)
+#include <sys/prctl.h>
+#endif
 
 /*
  * Reserve a new row if <first> is null, put it in the hotlist, set the refcount to 1
@@ -269,13 +272,14 @@ int shctx_row_data_get(struct shared_context *shctx, struct shared_block *first,
  * and 0 if cache is already allocated.
  */
 int shctx_init(struct shared_context **orig_shctx, int maxblocks, int blocksize,
-               unsigned int maxobjsz, int extra)
+               unsigned int maxobjsz, int extra, const char *name)
 {
 	int i;
 	struct shared_context *shctx;
 	int ret;
 	void *cur;
 	int maptype = MAP_SHARED;
+	size_t totalsize = sizeof(struct shared_context) + extra + (maxblocks * (sizeof(struct shared_block) + blocksize));
 
 	if (maxblocks <= 0)
 		return 0;
@@ -284,14 +288,38 @@ int shctx_init(struct shared_context **orig_shctx, int maxblocks, int blocksize,
 	blocksize = (blocksize + sizeof(void *) - 1) & -sizeof(void *);
 	extra     = (extra     + sizeof(void *) - 1) & -sizeof(void *);
 
-	shctx = (struct shared_context *)mmap(NULL, sizeof(struct shared_context) + extra + (maxblocks * (sizeof(struct shared_block) + blocksize)),
+	shctx = (struct shared_context *)mmap(NULL, totalsize, PROT_READ | PROT_WRITE, maptype | MAP_ANON, -1, 0);
-	                                      PROT_READ | PROT_WRITE, maptype | MAP_ANON, -1, 0);
 	if (!shctx || shctx == MAP_FAILED) {
 		shctx = NULL;
 		ret = SHCTX_E_ALLOC_CACHE;
 		goto err;
 	}
 
+#if defined(USE_PRCTL) && defined(PR_SET_VMA)
+	{
+		/**
+		 * From Linux 5.17 (and if the `CONFIG_ANON_VMA_NAME` kernel config is set)`,
+		 * anonymous regions can be named.
+		 * We intentionally ignore errors as it should not jeopardize the memory context
+		 * mapping whatsoever (e.g. older kernels).
+		 *
+		 * The naming can take up to 79 characters, accepting valid ASCII values
+		 * except [, ], \, $ and '.
+		 * As a result, when looking for /proc/<pid>/maps, we can see the anonymous range
+		 * as follow :
+		 * `7364c4fff000-736508000000 rw-s 00000000 00:01 3540  [anon_shmem:HAProxy globalCache]`
+		 */
+		int rn;
+		char fullname[80];
+
+		rn = snprintf(fullname, sizeof(fullname), "HAProxy %s", name);
+		if (rn >= 0) {
+			(void)prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, (uintptr_t)shctx,
+				totalsize, (uintptr_t)fullname);
+		}
+	}
+#endif
+
 	shctx->nbav = 0;
 
 	LIST_INIT(&shctx->avail);

src/ssl_sock.c

@@ -5351,7 +5351,7 @@ int ssl_sock_prepare_bind_conf(struct bind_conf *bind_conf)
 	if (!ssl_shctx && global.tune.sslcachesize) {
 		alloc_ctx = shctx_init(&ssl_shctx, global.tune.sslcachesize,
 		                       sizeof(struct sh_ssl_sess_hdr) + SHSESS_BLOCK_MIN_SIZE, -1,
-		                       sizeof(*sh_ssl_sess_tree));
+		                       sizeof(*sh_ssl_sess_tree), "ssl cache");
 		if (alloc_ctx <= 0) {
 			if (alloc_ctx == SHCTX_E_INIT_LOCK)
 				ha_alert("Unable to initialize the lock for the shared SSL session cache. You can retry using the global statement 'tune.ssl.force-private-cache' but it could increase CPU usage due to renegotiations if nbproc > 1.\n");