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x86/rtc: Don't recursively acquire rtc_lock 

A deadlock was introduced on x86 in commit ef68c8f87e ("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>
This commit is contained in:
Matt Fleming 2011-09-21 16:08:03 +02:00 committed by Ingo Molnar
parent 9d037a7776
commit 47997d756a
2 changed files with 21 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
arch/x86/kernel/rtc.c
View File

@ -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;

9
arch/x86/platform/mrst/vrtc.c
View File

@ -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;
}