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Commit 47997d75 authored by Matt Fleming's avatar Matt Fleming Committed by Ingo Molnar
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x86/rtc: Don't recursively acquire rtc_lock 



A deadlock was introduced on x86 in commit ef68c8f8 ("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: default avatarMatt Fleming <matt.fleming@intel.com>
Acked-by: default avatarJan 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 9d037a77

arch/x86/kernel/rtc.c

+12 −11
Original line number Original line Diff line number Diff line
@@ -42,8 +42,11 @@ int mach_set_rtc_mmss(unsigned long nowtime) 
{

{

	int real_seconds, real_minutes, cmos_minutes;

	int real_seconds, real_minutes, cmos_minutes;

	unsigned char save_control, save_freq_select;

	unsigned char save_control, save_freq_select;

	unsigned long flags;

	int retval = 0;

	int retval = 0;





	spin_lock_irqsave(&rtc_lock, flags);



	 /* tell the clock it's being set */

	 /* tell the clock it's being set */

	save_control = CMOS_READ(RTC_CONTROL);

	save_control = CMOS_READ(RTC_CONTROL);

	CMOS_WRITE((save_control|RTC_SET), 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_control, RTC_CONTROL);

	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);

	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);





	spin_unlock_irqrestore(&rtc_lock, flags);



	return retval;

	return retval;

}

}





unsigned long mach_get_cmos_time(void)

unsigned long mach_get_cmos_time(void)

{

{

	unsigned int status, year, mon, day, hour, min, sec, century = 0;

	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

	 * 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);

	status = CMOS_READ(RTC_CONTROL);

	WARN_ON_ONCE(RTC_ALWAYS_BCD && (status & RTC_DM_BINARY));

	WARN_ON_ONCE(RTC_ALWAYS_BCD && (status & RTC_DM_BINARY));





	spin_unlock_irqrestore(&rtc_lock, flags);



	if (RTC_ALWAYS_BCD || !(status & RTC_DM_BINARY)) {

	if (RTC_ALWAYS_BCD || !(status & RTC_DM_BINARY)) {

		sec = bcd2bin(sec);

		sec = bcd2bin(sec);

		min = bcd2bin(min);

		min = bcd2bin(min);
@@ -169,24 +179,15 @@ EXPORT_SYMBOL(rtc_cmos_write); 




int update_persistent_clock(struct timespec now)

int update_persistent_clock(struct timespec now)

{

{

	unsigned long flags;

	return x86_platform.set_wallclock(now.tv_sec);

	int retval;



	spin_lock_irqsave(&rtc_lock, flags);

	retval = x86_platform.set_wallclock(now.tv_sec);

	spin_unlock_irqrestore(&rtc_lock, flags);



	return retval;

}

}





/* not static: needed by APM */

/* not static: needed by APM */

void read_persistent_clock(struct timespec *ts)

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();

	retval = x86_platform.get_wallclock();

	spin_unlock_irqrestore(&rtc_lock, flags);





	ts->tv_sec = retval;

	ts->tv_sec = retval;

	ts->tv_nsec = 0;

	ts->tv_nsec = 0;

arch/x86/platform/mrst/vrtc.c

+9 −0
Original line number Original line Diff line number Diff line
@@ -58,8 +58,11 @@ EXPORT_SYMBOL_GPL(vrtc_cmos_write); 
unsigned long vrtc_get_time(void)

unsigned long vrtc_get_time(void)

{

{

	u8 sec, min, hour, mday, mon;

	u8 sec, min, hour, mday, mon;

	unsigned long flags;

	u32 year;

	u32 year;





	spin_lock_irqsave(&rtc_lock, flags);



	while ((vrtc_cmos_read(RTC_FREQ_SELECT) & RTC_UIP))

	while ((vrtc_cmos_read(RTC_FREQ_SELECT) & RTC_UIP))

		cpu_relax();

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

	mon = vrtc_cmos_read(RTC_MONTH);

	year = vrtc_cmos_read(RTC_YEAR);

	year = vrtc_cmos_read(RTC_YEAR);





	spin_unlock_irqrestore(&rtc_lock, flags);



	/* vRTC YEAR reg contains the offset to 1960 */

	/* vRTC YEAR reg contains the offset to 1960 */

	year += 1960;

	year += 1960;
@@ -83,8 +88,10 @@ unsigned long vrtc_get_time(void) 
int vrtc_set_mmss(unsigned long nowtime)

int vrtc_set_mmss(unsigned long nowtime)

{

{

	int real_sec, real_min;

	int real_sec, real_min;

	unsigned long flags;

	int vrtc_min;

	int vrtc_min;





	spin_lock_irqsave(&rtc_lock, flags);

	vrtc_min = vrtc_cmos_read(RTC_MINUTES);

	vrtc_min = vrtc_cmos_read(RTC_MINUTES);





	real_sec = nowtime % 60;

	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_sec, RTC_SECONDS);

	vrtc_cmos_write(real_min, RTC_MINUTES);

	vrtc_cmos_write(real_min, RTC_MINUTES);

	spin_unlock_irqrestore(&rtc_lock, flags);



	return 0;

	return 0;

}

}