From: Zwane Mwaikambo <zwane@linuxpower.ca>
The following patch from Shaohua Li fixes a race with preempt enabled when
a module containing a pm_idle callback is unloaded. Cached values in local
variables need to be protected as RCU critical sections so that the
synchronize_kernel() call in the unload path waits for all processors.
There original bugzilla entry can be found at
Shaohua, i had to make a small change (variable declaration after code in
code block) so that it compiles with geriatric compilers such as the ones
Andrew is attached to ;)
http://bugzilla.kernel.org/show_bug.cgi?id=1716
Signed-off-by: Li Shaohua <shaohua.li@intel.com>
Signed-off-by: Zwane Mwaikambo <zwane@linuxpower.ca>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/arch/i386/kernel/apm.c | 9 ++++++++-
25-akpm/arch/i386/kernel/process.c | 10 +++++++++-
25-akpm/arch/ia64/kernel/process.c | 16 ++++++++++++----
25-akpm/arch/x86_64/kernel/process.c | 17 +++++++++++++----
25-akpm/drivers/acpi/processor.c | 5 +++++
5 files changed, 47 insertions(+), 10 deletions(-)
diff -puN arch/i386/kernel/apm.c~close-race-with-preempt-and-modular-pm_idle-callbacks arch/i386/kernel/apm.c
--- 25/arch/i386/kernel/apm.c~close-race-with-preempt-and-modular-pm_idle-callbacks Thu Sep 9 15:41:44 2004
+++ 25-akpm/arch/i386/kernel/apm.c Thu Sep 9 15:41:45 2004
@@ -2362,8 +2362,15 @@ static void __exit apm_exit(void)
{
int error;
- if (set_pm_idle)
+ if (set_pm_idle) {
pm_idle = original_pm_idle;
+ /*
+ * We are about to unload the current idle thread pm callback
+ * (pm_idle), Wait for all processors to update cached/local
+ * copies of pm_idle before proceeding.
+ */
+ synchronize_kernel();
+ }
if (((apm_info.bios.flags & APM_BIOS_DISENGAGED) == 0)
&& (apm_info.connection_version > 0x0100)) {
error = apm_engage_power_management(APM_DEVICE_ALL, 0);
diff -puN arch/i386/kernel/process.c~close-race-with-preempt-and-modular-pm_idle-callbacks arch/i386/kernel/process.c
--- 25/arch/i386/kernel/process.c~close-race-with-preempt-and-modular-pm_idle-callbacks Thu Sep 9 15:41:44 2004
+++ 25-akpm/arch/i386/kernel/process.c Thu Sep 9 15:41:45 2004
@@ -175,7 +175,14 @@ void cpu_idle (void)
/* endless idle loop with no priority at all */
while (1) {
while (!need_resched()) {
- void (*idle)(void) = pm_idle;
+ void (*idle)(void);
+ /*
+ * Mark this as an RCU critical section so that
+ * synchronize_kernel() in the unload path waits
+ * for our completion.
+ */
+ rcu_read_lock();
+ idle = pm_idle;
if (!idle)
idle = default_idle;
@@ -184,6 +191,7 @@ void cpu_idle (void)
play_dead();
irq_stat[smp_processor_id()].idle_timestamp = jiffies;
idle();
+ rcu_read_unlock();
}
schedule();
}
diff -puN arch/ia64/kernel/process.c~close-race-with-preempt-and-modular-pm_idle-callbacks arch/ia64/kernel/process.c
--- 25/arch/ia64/kernel/process.c~close-race-with-preempt-and-modular-pm_idle-callbacks Thu Sep 9 15:41:45 2004
+++ 25-akpm/arch/ia64/kernel/process.c Thu Sep 9 15:41:45 2004
@@ -228,18 +228,26 @@ cpu_idle (void *unused)
/* endless idle loop with no priority at all */
while (1) {
- void (*idle)(void) = pm_idle;
- if (!idle)
- idle = default_idle;
-
#ifdef CONFIG_SMP
if (!need_resched())
min_xtp();
#endif
while (!need_resched()) {
+ void (*idle)(void);
+
if (mark_idle)
(*mark_idle)(1);
+ /*
+ * Mark this as an RCU critical section so that
+ * synchronize_kernel() in the unload path waits
+ * for our completion.
+ */
+ rcu_read_lock();
+ idle = pm_idle;
+ if (!idle)
+ idle = default_idle;
(*idle)();
+ rcu_read_unlock();
}
if (mark_idle)
diff -puN arch/x86_64/kernel/process.c~close-race-with-preempt-and-modular-pm_idle-callbacks arch/x86_64/kernel/process.c
--- 25/arch/x86_64/kernel/process.c~close-race-with-preempt-and-modular-pm_idle-callbacks Thu Sep 9 15:41:45 2004
+++ 25-akpm/arch/x86_64/kernel/process.c Thu Sep 9 15:41:45 2004
@@ -131,11 +131,20 @@ void cpu_idle (void)
{
/* endless idle loop with no priority at all */
while (1) {
- void (*idle)(void) = pm_idle;
- if (!idle)
- idle = default_idle;
- while (!need_resched())
+ while (!need_resched()) {
+ void (*idle)(void);
+ /*
+ * Mark this as an RCU critical section so that
+ * synchronize_kernel() in the unload path waits
+ * for our completion.
+ */
+ rcu_read_lock();
+ idle = pm_idle;
+ if (!idle)
+ idle = default_idle;
idle();
+ rcu_read_unlock();
+ }
schedule();
}
}
diff -puN drivers/acpi/processor.c~close-race-with-preempt-and-modular-pm_idle-callbacks drivers/acpi/processor.c
--- 25/drivers/acpi/processor.c~close-race-with-preempt-and-modular-pm_idle-callbacks Thu Sep 9 15:41:45 2004
+++ 25-akpm/drivers/acpi/processor.c Thu Sep 9 15:41:45 2004
@@ -2424,6 +2424,11 @@ acpi_processor_remove (
/* Unregister the idle handler when processor #0 is removed. */
if (pr->id == 0) {
pm_idle = pm_idle_save;
+ /*
+ * We are about to unload the current idle thread pm callback
+ * (pm_idle), Wait for all processors to update cached/local
+ * copies of pm_idle before proceeding.
+ */
synchronize_kernel();
}
_