From: Willy Tarreau <w@1wt.eu>
Date: Fri, 1 Oct 2021 14:29:27 +0000 (+0200)
Subject: MINOR: thread: make "ti" a const pointer and clean up thread_info a bit
X-Git-Tag: v2.5-dev9~15
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6036342f58bb350e4d95cb63d1567439b71165b7;p=thirdparty%2Fhaproxy.git

MINOR: thread: make "ti" a const pointer and clean up thread_info a bit

We want to make sure that the current thread_info accessed via "ti" will
remain constant, so that we don't accidentally place new variable parts
there and so that the compiler knows that info retrieved from there is
not expected to have changed between two function calls.

Only a few init locations had to be adjusted to use the array and the
rest is unaffected.
---

diff --git a/include/haproxy/tinfo-t.h b/include/haproxy/tinfo-t.h
index 737431f7a3..fe9ef9bd02 100644
--- a/include/haproxy/tinfo-t.h
+++ b/include/haproxy/tinfo-t.h
@@ -39,11 +39,13 @@ enum {
 #define TH_FL_STUCK             0x00000001
 
 /* This structure describes all the per-thread info we need. When threads are
- * disabled, it contains the same info for the single running thread.
+ * disabled, it contains the same info for the single running thread. This is
+ * stable across all of a thread's life, and is being pointed to by the
+ * thread-local "ti" pointer.
  */
 struct thread_info {
 	/* pad to cache line (64B) */
-	char __pad[0];            /* unused except to check remaining room */
+	char __pad[0];                    /* unused except to check remaining room */
 	char __end[0] __attribute__((aligned(64)));
 };
 
diff --git a/include/haproxy/tinfo.h b/include/haproxy/tinfo.h
index 6e73824cb5..a1b73463f0 100644
--- a/include/haproxy/tinfo.h
+++ b/include/haproxy/tinfo.h
@@ -27,7 +27,7 @@
 
 /* the structs are in thread.c */
 extern struct thread_info ha_thread_info[MAX_THREADS];
-extern THREAD_LOCAL struct thread_info *ti; /* thread_info for the current thread */
+extern THREAD_LOCAL const struct thread_info *ti;   /* thread_info for the current thread */
 
 extern struct thread_ctx ha_thread_ctx[MAX_THREADS];
 extern THREAD_LOCAL struct thread_ctx *th_ctx; /* ha_thread_ctx for the current thread */
diff --git a/src/thread.c b/src/thread.c
index ab9ef90b65..14bf21eba6 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -51,7 +51,7 @@
 #include <haproxy/tools.h>
 
 struct thread_info ha_thread_info[MAX_THREADS] = { };
-THREAD_LOCAL struct thread_info *ti = &ha_thread_info[0];
+THREAD_LOCAL const struct thread_info *ti = &ha_thread_info[0];
 
 struct thread_ctx ha_thread_ctx[MAX_THREADS] = { };
 THREAD_LOCAL struct thread_ctx *th_ctx = &ha_thread_ctx[0];