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authorLai Jiangshan <laijs@cn.fujitsu.com>2009-03-18 16:42:57 +0800
committerSteven Rostedt <srostedt@redhat.com>2009-03-18 20:36:59 -0400
commite9d9df44736d116726f4596f7e2f9ce2764ffc0a (patch)
treebca129639885fa7288b925e5053f3787fa7e625a
parent4acd4d00f716873e27e7b60ae292cbdbfae674dd (diff)
ftrace: protect running nmi (V3)
When I review the sensitive code ftrace_nmi_enter(), I found the atomic variable nmi_running does protect NMI VS do_ftrace_mod_code(), but it can not protects NMI(entered nmi) VS NMI(ftrace_nmi_enter()). cpu#1 | cpu#2 | cpu#3 ftrace_nmi_enter() | do_ftrace_mod_code() | not modify | | ------------------------|-----------------------|-- executing | set mod_code_write = 1| executing --|-----------------------|-------------------- executing | | ftrace_nmi_enter() executing | | do modify ------------------------|-----------------------|----------------- ftrace_nmi_exit() | | cpu#3 may be being modified the code which is still being executed on cpu#1, it will have undefined results and possibly take a GPF, this patch prevents it occurred. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> LKML-Reference: <49C0B411.30003@cn.fujitsu.com> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
-rw-r--r--arch/x86/kernel/ftrace.c63
1 files changed, 40 insertions, 23 deletions
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 1d0d7f42efe..57b33edb7ce 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -79,11 +79,11 @@ static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
*
* 1) Put the instruction pointer into the IP buffer
* and the new code into the "code" buffer.
- * 2) Set a flag that says we are modifying code
- * 3) Wait for any running NMIs to finish.
- * 4) Write the code
- * 5) clear the flag.
- * 6) Wait for any running NMIs to finish.
+ * 2) Wait for any running NMIs to finish and set a flag that says
+ * we are modifying code, it is done in an atomic operation.
+ * 3) Write the code
+ * 4) clear the flag.
+ * 5) Wait for any running NMIs to finish.
*
* If an NMI is executed, the first thing it does is to call
* "ftrace_nmi_enter". This will check if the flag is set to write
@@ -95,9 +95,9 @@ static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
* are the same as what exists.
*/
+#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
static atomic_t nmi_running = ATOMIC_INIT(0);
static int mod_code_status; /* holds return value of text write */
-static int mod_code_write; /* set when NMI should do the write */
static void *mod_code_ip; /* holds the IP to write to */
static void *mod_code_newcode; /* holds the text to write to the IP */
@@ -114,6 +114,20 @@ int ftrace_arch_read_dyn_info(char *buf, int size)
return r;
}
+static void clear_mod_flag(void)
+{
+ int old = atomic_read(&nmi_running);
+
+ for (;;) {
+ int new = old & ~MOD_CODE_WRITE_FLAG;
+
+ if (old == new)
+ break;
+
+ old = atomic_cmpxchg(&nmi_running, old, new);
+ }
+}
+
static void ftrace_mod_code(void)
{
/*
@@ -127,27 +141,39 @@ static void ftrace_mod_code(void)
/* if we fail, then kill any new writers */
if (mod_code_status)
- mod_code_write = 0;
+ clear_mod_flag();
}
void ftrace_nmi_enter(void)
{
- atomic_inc(&nmi_running);
- /* Must have nmi_running seen before reading write flag */
- smp_mb();
- if (mod_code_write) {
+ if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
+ smp_rmb();
ftrace_mod_code();
atomic_inc(&nmi_update_count);
}
+ /* Must have previous changes seen before executions */
+ smp_mb();
}
void ftrace_nmi_exit(void)
{
/* Finish all executions before clearing nmi_running */
- smp_wmb();
+ smp_mb();
atomic_dec(&nmi_running);
}
+static void wait_for_nmi_and_set_mod_flag(void)
+{
+ if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
+ return;
+
+ do {
+ cpu_relax();
+ } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
+
+ nmi_wait_count++;
+}
+
static void wait_for_nmi(void)
{
if (!atomic_read(&nmi_running))
@@ -167,14 +193,9 @@ do_ftrace_mod_code(unsigned long ip, void *new_code)
mod_code_newcode = new_code;
/* The buffers need to be visible before we let NMIs write them */
- smp_wmb();
-
- mod_code_write = 1;
-
- /* Make sure write bit is visible before we wait on NMIs */
smp_mb();
- wait_for_nmi();
+ wait_for_nmi_and_set_mod_flag();
/* Make sure all running NMIs have finished before we write the code */
smp_mb();
@@ -182,13 +203,9 @@ do_ftrace_mod_code(unsigned long ip, void *new_code)
ftrace_mod_code();
/* Make sure the write happens before clearing the bit */
- smp_wmb();
-
- mod_code_write = 0;
-
- /* make sure NMIs see the cleared bit */
smp_mb();
+ clear_mod_flag();
wait_for_nmi();
return mod_code_status;