[PATCH] [4/9] SYSCTL: Use RCU strings for core_pattern sysctl

[Andi Kleen]

Also saves ~220 bytes in the data segment for default kernels.

As a bonus this removes one use of the BKL.

Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>

---
 fs/exec.c       |   11 +++++------
 kernel/sysctl.c |    6 +++---
 2 files changed, 8 insertions(+), 9 deletions(-)

Index: linux-2.6.33-rc2-ak/fs/exec.c
===================================================================
--- linux-2.6.33-rc2-ak.orig/fs/exec.c
+++ linux-2.6.33-rc2-ak/fs/exec.c
@@ -62,7 +62,7 @@
 #include "internal.h"
 
 int core_uses_pid;
-char core_pattern[CORENAME_MAX_SIZE] = "core";
+char *core_pattern = "core";
 unsigned int core_pipe_limit;
 int suid_dumpable = 0;
 
@@ -1421,7 +1421,7 @@ EXPORT_SYMBOL(set_binfmt);
 static int format_corename(char *corename, long signr)
 {
 	const struct cred *cred = current_cred();
-	const char *pat_ptr = core_pattern;
+	const char *pat_ptr = rcu_dereference(core_pattern);
 	int ispipe = (*pat_ptr == '|');
 	char *out_ptr = corename;
 	char *const out_end = corename + CORENAME_MAX_SIZE;
@@ -1825,12 +1825,11 @@ void do_coredump(long signr, int exit_co
 	clear_thread_flag(TIF_SIGPENDING);
 
 	/*
-	 * lock_kernel() because format_corename() is controlled by sysctl, which
-	 * uses lock_kernel()
+	 * Protect corename by RCU vs proc_rcu_string()
 	 */
- 	lock_kernel();
+	rcu_read_lock();
 	ispipe = format_corename(corename, signr);
-	unlock_kernel();
+	rcu_read_unlock();
 
 	if ((!ispipe) && (cprm.limit < binfmt->min_coredump))
 		goto fail_unlock;
Index: linux-2.6.33-rc2-ak/kernel/sysctl.c
===================================================================
--- linux-2.6.33-rc2-ak.orig/kernel/sysctl.c
+++ linux-2.6.33-rc2-ak/kernel/sysctl.c
@@ -75,7 +75,7 @@ extern int sysctl_oom_dump_tasks;
 extern int max_threads;
 extern int core_uses_pid;
 extern int suid_dumpable;
-extern char core_pattern[];
+extern char *core_pattern;
 extern unsigned int core_pipe_limit;
 extern int pid_max;
 extern int min_free_kbytes;
@@ -399,10 +399,10 @@ static struct ctl_table kern_table[] = {
 	},
 	{
 		.procname	= "core_pattern",
-		.data		= core_pattern,
+		.data		= &core_pattern,
 		.maxlen		= CORENAME_MAX_SIZE,
 		.mode		= 0644,
-		.proc_handler	= proc_dostring,
+		.proc_handler	= proc_rcu_string,
 	},
 	{
 		.procname	= "core_pipe_limit",
--
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