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Subject[patch 3/4] x86: vdso: Use seqcount instead of seqlock
The update of the vdso data happens under xtime_lock, so adding a
nested lock is pointless. Just use a seqcount to sync the readers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/include/asm/vgtod.h | 2 +-
arch/x86/kernel/vsyscall_64.c | 11 +++--------
arch/x86/vdso/vclock_gettime.c | 16 ++++++++--------
3 files changed, 12 insertions(+), 17 deletions(-)

Index: linux-2.6/arch/x86/include/asm/vgtod.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/vgtod.h
+++ linux-2.6/arch/x86/include/asm/vgtod.h
@@ -5,7 +5,7 @@
#include <linux/clocksource.h>

struct vsyscall_gtod_data {
- seqlock_t lock;
+ seqcount_t seq;

/* open coded 'struct timespec' */
time_t wall_time_sec;
Index: linux-2.6/arch/x86/kernel/vsyscall_64.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/vsyscall_64.c
+++ linux-2.6/arch/x86/kernel/vsyscall_64.c
@@ -52,10 +52,7 @@
#include "vsyscall_trace.h"

DEFINE_VVAR(int, vgetcpu_mode);
-DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
-{
- .lock = __SEQLOCK_UNLOCKED(__vsyscall_gtod_data.lock),
-};
+DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data);

static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;

@@ -86,9 +83,7 @@ void update_vsyscall_tz(void)
void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
struct clocksource *clock, u32 mult)
{
- unsigned long flags;
-
- write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
+ write_seqcount_begin(&vsyscall_gtod_data.seq);

/* copy vsyscall data */
vsyscall_gtod_data.clock.vclock_mode = clock->archdata.vclock_mode;
@@ -101,7 +96,7 @@ void update_vsyscall(struct timespec *wa
vsyscall_gtod_data.wall_to_monotonic = *wtm;
vsyscall_gtod_data.wall_time_coarse = __current_kernel_time();

- write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
+ write_seqcount_end(&vsyscall_gtod_data.seq);
}

static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
Index: linux-2.6/arch/x86/vdso/vclock_gettime.c
===================================================================
--- linux-2.6.orig/arch/x86/vdso/vclock_gettime.c
+++ linux-2.6/arch/x86/vdso/vclock_gettime.c
@@ -86,11 +86,11 @@ notrace static noinline int do_realtime(
{
unsigned long seq, ns;
do {
- seq = read_seqbegin(&gtod->lock);
+ seq = read_seqcount_begin(&gtod->seq);
ts->tv_sec = gtod->wall_time_sec;
ts->tv_nsec = gtod->wall_time_nsec;
ns = vgetns();
- } while (unlikely(read_seqretry(&gtod->lock, seq)));
+ } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
timespec_add_ns(ts, ns);
return 0;
}
@@ -99,12 +99,12 @@ notrace static noinline int do_monotonic
{
unsigned long seq, ns, secs;
do {
- seq = read_seqbegin(&gtod->lock);
+ seq = read_seqcount_begin(&gtod->seq);
secs = gtod->wall_time_sec;
ns = gtod->wall_time_nsec + vgetns();
secs += gtod->wall_to_monotonic.tv_sec;
ns += gtod->wall_to_monotonic.tv_nsec;
- } while (unlikely(read_seqretry(&gtod->lock, seq)));
+ } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));

/* wall_time_nsec, vgetns(), and wall_to_monotonic.tv_nsec
* are all guaranteed to be nonnegative.
@@ -123,10 +123,10 @@ notrace static noinline int do_realtime_
{
unsigned long seq;
do {
- seq = read_seqbegin(&gtod->lock);
+ seq = read_seqcount_begin(&gtod->seq);
ts->tv_sec = gtod->wall_time_coarse.tv_sec;
ts->tv_nsec = gtod->wall_time_coarse.tv_nsec;
- } while (unlikely(read_seqretry(&gtod->lock, seq)));
+ } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
return 0;
}

@@ -134,12 +134,12 @@ notrace static noinline int do_monotonic
{
unsigned long seq, ns, secs;
do {
- seq = read_seqbegin(&gtod->lock);
+ seq = read_seqcount_begin(&gtod->seq);
secs = gtod->wall_time_coarse.tv_sec;
ns = gtod->wall_time_coarse.tv_nsec;
secs += gtod->wall_to_monotonic.tv_sec;
ns += gtod->wall_to_monotonic.tv_nsec;
- } while (unlikely(read_seqretry(&gtod->lock, seq)));
+ } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));

/* wall_time_nsec and wall_to_monotonic.tv_nsec are
* guaranteed to be between 0 and NSEC_PER_SEC.



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