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Commit 2ab51657 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by John Stultz
Browse files

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.

Reviewed-by: default avatarAndy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
parent 6c260d58

arch/x86/include/asm/vgtod.h

+1 −1
Original line number Diff line number Diff line
@@ -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;

arch/x86/kernel/vsyscall_64.c

+3 −8
Original line number Diff line number Diff line
@@ -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,

arch/x86/vdso/vclock_gettime.c

+8 −8
Original line number Diff line number Diff line
@@ -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.