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Subject[PATCH v2] x86: Don't recursively acquire rtc_lock
Date
From: Matt Fleming <matt.fleming@intel.com>

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]
---
arch/x86/kernel/rtc.c | 23 ++++++++++++-----------
arch/x86/platform/mrst/vrtc.c | 9 +++++++++
2 files changed, 21 insertions(+), 11 deletions(-)

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 mach_set_rtc_mmss(unsigned long nowtime)
{
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 @@ int mach_set_rtc_mmss(unsigned long nowtime)
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 @@ unsigned long mach_get_cmos_time(void)
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 @@ EXPORT_SYMBOL(rtc_cmos_write);

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;
diff --git a/arch/x86/platform/mrst/vrtc.c b/arch/x86/platform/mrst/vrtc.c
index 73d70d6..6d5dbcd 100644
--- a/arch/x86/platform/mrst/vrtc.c
+++ b/arch/x86/platform/mrst/vrtc.c
@@ -58,8 +58,11 @@ EXPORT_SYMBOL_GPL(vrtc_cmos_write);
unsigned long vrtc_get_time(void)
{
u8 sec, min, hour, mday, mon;
+ unsigned long flags;
u32 year;

+ spin_lock_irqsave(&rtc_lock, flags);
+
while ((vrtc_cmos_read(RTC_FREQ_SELECT) & RTC_UIP))
cpu_relax();

@@ -70,6 +73,8 @@ unsigned long vrtc_get_time(void)
mon = vrtc_cmos_read(RTC_MONTH);
year = vrtc_cmos_read(RTC_YEAR);

+ spin_unlock_irqrestore(&rtc_lock, flags);
+
/* vRTC YEAR reg contains the offset to 1960 */
year += 1960;

@@ -83,8 +88,10 @@ unsigned long vrtc_get_time(void)
int vrtc_set_mmss(unsigned long nowtime)
{
int real_sec, real_min;
+ unsigned long flags;
int vrtc_min;

+ spin_lock_irqsave(&rtc_lock, flags);
vrtc_min = vrtc_cmos_read(RTC_MINUTES);

real_sec = nowtime % 60;
@@ -95,6 +102,8 @@ int vrtc_set_mmss(unsigned long nowtime)

vrtc_cmos_write(real_sec, RTC_SECONDS);
vrtc_cmos_write(real_min, RTC_MINUTES);
+ spin_unlock_irqrestore(&rtc_lock, flags);
+
return 0;
}

--
1.7.4.4


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