x86/rtc: Don't recursively acquire rtc_lock
A deadlock was introduced on x86 in commit ef68c8f87ed1 ("x86:
Serialize EFI time accesses on rtc_lock") because efi_get_time()
and friends can be called with rtc_lock already held by
read_persistent_time(), e.g.:
timekeeping_init()
read_persistent_clock() <-- acquire rtc_lock
efi_get_time()
phys_efi_get_time() <-- acquire rtc_lock <DEADLOCK>
To fix this let's push the locking down into the get_wallclock()
and set_wallclock() implementations. Only the clock
implementations that access the x86 RTC directly need to acquire
rtc_lock, so it makes sense to push the locking down into the
rtc, vrtc and efi code.
The virtualization implementations don't require rtc_lock to be
held because they provide their own serialization.
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Acked-by: Jan Beulich <jbeulich@novell.com>
Acked-by: Avi Kivity <avi@redhat.com> [for the virtualization aspect]
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Josh Boyer <jwboyer@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
index 3f2ad26..ccdbc16 100644
--- a/arch/x86/kernel/rtc.c
+++ b/arch/x86/kernel/rtc.c
@@ -42,8 +42,11 @@
{
int real_seconds, real_minutes, cmos_minutes;
unsigned char save_control, save_freq_select;
+ unsigned long flags;
int retval = 0;
+ spin_lock_irqsave(&rtc_lock, flags);
+
/* tell the clock it's being set */
save_control = CMOS_READ(RTC_CONTROL);
CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
@@ -93,12 +96,17 @@
CMOS_WRITE(save_control, RTC_CONTROL);
CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
+ spin_unlock_irqrestore(&rtc_lock, flags);
+
return retval;
}
unsigned long mach_get_cmos_time(void)
{
unsigned int status, year, mon, day, hour, min, sec, century = 0;
+ unsigned long flags;
+
+ spin_lock_irqsave(&rtc_lock, flags);
/*
* If UIP is clear, then we have >= 244 microseconds before
@@ -125,6 +133,8 @@
status = CMOS_READ(RTC_CONTROL);
WARN_ON_ONCE(RTC_ALWAYS_BCD && (status & RTC_DM_BINARY));
+ spin_unlock_irqrestore(&rtc_lock, flags);
+
if (RTC_ALWAYS_BCD || !(status & RTC_DM_BINARY)) {
sec = bcd2bin(sec);
min = bcd2bin(min);
@@ -169,24 +179,15 @@
int update_persistent_clock(struct timespec now)
{
- unsigned long flags;
- int retval;
-
- spin_lock_irqsave(&rtc_lock, flags);
- retval = x86_platform.set_wallclock(now.tv_sec);
- spin_unlock_irqrestore(&rtc_lock, flags);
-
- return retval;
+ return x86_platform.set_wallclock(now.tv_sec);
}
/* not static: needed by APM */
void read_persistent_clock(struct timespec *ts)
{
- unsigned long retval, flags;
+ unsigned long retval;
- spin_lock_irqsave(&rtc_lock, flags);
retval = x86_platform.get_wallclock();
- spin_unlock_irqrestore(&rtc_lock, flags);
ts->tv_sec = retval;
ts->tv_nsec = 0;
