The patch titled
x86 rtc: don't recursively acquire rtc_lock
has been added to the -mm tree. Its filename is
x86-rtc-dont-recursively-acquire-rtc_lock.patch
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See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: x86 rtc: don't recursively acquire rtc_lock
From: Matt Fleming <matt.fleming@xxxxxxxxx>
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@xxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Acked-by: Avi Kivity <avi@xxxxxxxxxx> [for the virtualization aspect]
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Zhang Rui <rui.zhang@xxxxxxxxx>
Cc: Josh Boyer <jwboyer@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/rtc.c | 23 ++++++++++++-----------
arch/x86/platform/mrst/vrtc.c | 9 +++++++++
2 files changed, 21 insertions(+), 11 deletions(-)
diff -puN arch/x86/kernel/rtc.c~x86-rtc-dont-recursively-acquire-rtc_lock arch/x86/kernel/rtc.c
--- a/arch/x86/kernel/rtc.c~x86-rtc-dont-recursively-acquire-rtc_lock
+++ a/arch/x86/kernel/rtc.c
@@ -43,8 +43,11 @@ int mach_set_rtc_mmss(unsigned long nowt
{
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);
@@ -94,12 +97,17 @@ int mach_set_rtc_mmss(unsigned long nowt
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
@@ -126,6 +134,8 @@ 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);
@@ -170,24 +180,15 @@ 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 -puN arch/x86/platform/mrst/vrtc.c~x86-rtc-dont-recursively-acquire-rtc_lock arch/x86/platform/mrst/vrtc.c
--- a/arch/x86/platform/mrst/vrtc.c~x86-rtc-dont-recursively-acquire-rtc_lock
+++ a/arch/x86/platform/mrst/vrtc.c
@@ -59,8 +59,11 @@ 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();
@@ -71,6 +74,8 @@ 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;
@@ -84,8 +89,10 @@ 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;
@@ -96,6 +103,8 @@ 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;
}
_
Patches currently in -mm which might be from matt.fleming@xxxxxxxxx are
linux-next.patch
x86-rtc-dont-recursively-acquire-rtc_lock.patch
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