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x86: vdso: Use seqcount instead of seqlock

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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.

Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
This commit is contained in:
Thomas Gleixner 2012-02-28 19:46:04 +00:00 committed by John Stultz
parent 6c260d5863
commit 2ab516575f
3 changed files with 12 additions and 17 deletions
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2
arch/x86/include/asm/vgtod.h
View File

@ -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;

11
arch/x86/kernel/vsyscall_64.c
View File

@ -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 *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,

16
arch/x86/vdso/vclock_gettime.c
View File

@ -100,12 +100,12 @@ notrace static noinline int do_realtime(struct timespec *ts)
int mode;
do {
seq = read_seqbegin(&gtod->lock);
seq = read_seqcount_begin(&gtod->seq);
mode = gtod->clock.vclock_mode;
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 mode;
@ -117,13 +117,13 @@ notrace static noinline int do_monotonic(struct timespec *ts)
int mode;
do {
seq = read_seqbegin(&gtod->lock);
seq = read_seqcount_begin(&gtod->seq);
mode = gtod->clock.vclock_mode;
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.
@ -142,10 +142,10 @@ 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;
}
@ -153,12 +153,12 @@ 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.