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Subject[PATCH RT 08/25][RFC 3.0.23-rt39-rc1] x86: vdso: Use seqcount instead of seqlock
From: Thomas Gleixner <tglx@linutronix.de>

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>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
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(-)
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h
index 646b4c1..10e09fc 100644
--- a/arch/x86/include/asm/vgtod.h
+++ b/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;
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index c378a18..c1fe684 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -50,11 +50,7 @@
#include <asm/traps.h>

DEFINE_VVAR(int, vgetcpu_mode);
-DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
-{
- .lock = __SEQLOCK_UNLOCKED(__vsyscall_gtod_data.lock),
- .sysctl_enabled = 1,
-};
+DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data);

void update_vsyscall_tz(void)
{
@@ -64,9 +60,8 @@ void update_vsyscall_tz(void)
void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
struct clocksource *clock, u32 mult)
{
- unsigned long flags;
+ write_seqcount_begin(&vsyscall_gtod_data.seq);

- write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);

/* copy vsyscall data */
vsyscall_gtod_data.clock.vread = clock->vread;
@@ -79,7 +74,7 @@ void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
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,
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index a724905..117e6cf 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -46,11 +46,11 @@ notrace static noinline int do_realtime(struct timespec *ts)
{
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;
}
@@ -59,12 +59,12 @@ notrace static noinline int do_monotonic(struct timespec *ts)
{
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.
@@ -83,10 +83,10 @@ notrace static noinline int do_realtime_coarse(struct timespec *ts)
{
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;
}

@@ -94,12 +94,12 @@ notrace static noinline int do_monotonic_coarse(struct timespec *ts)
{
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.
--
1.7.8.3



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