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

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@linux.intel.com>

---
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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