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: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: John Stultz <john.stultz@linaro.org>

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: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: John Stultz <john.stultz@linaro.org>
Thomas Gleixner · John Stultz
1 parent 6c260d5863
Showing 3 changed files with 12 additions and 17 deletions Side-by-side Diff
arch/x86/include/asm/vgtod.h
arch/x86/kernel/vsyscall_64.c
arch/x86/vdso/vclock_gettime.c
@@ -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;
@@ -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;
  
  
@@ -86,10 +83,8 @@
 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.vclock_mode	= clock->archdata.vclock_mode;
 	vsyscall_gtod_data.clock.cycle_last	= clock->cycle_last;
@@ -101,7 +96,7 @@
 	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,
@@ -100,12 +100,12 @@
 	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 @@
 	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 @@
 {
 	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 @@
 {
 	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.
...	...	@@ -5,7 +5,7 @@
5	5	#include <linux/clocksource.h>
6	6
7	7	struct vsyscall_gtod_data {
8		- seqlock_t lock;
	8	+ seqcount_t seq;
9	9
10	10	/* open coded 'struct timespec' */
11	11	time_t wall_time_sec;
...	...	@@ -52,10 +52,7 @@
52	52	#include "vsyscall_trace.h"
53	53
54	54	DEFINE_VVAR(int, vgetcpu_mode);
55		-DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
56		-{
57		- .lock = __SEQLOCK_UNLOCKED(__vsyscall_gtod_data.lock),
58		-};
	55	+DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data);
59	56
60	57	static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;
61	58
62	59
...	...	@@ -86,10 +83,8 @@
86	83	void update_vsyscall(struct timespec wall_time, struct timespec wtm,
87	84	struct clocksource *clock, u32 mult)
88	85	{
89		- unsigned long flags;
	86	+ write_seqcount_begin(&vsyscall_gtod_data.seq);
90	87
91		- write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
92		-
93	88	/* copy vsyscall data */
94	89	vsyscall_gtod_data.clock.vclock_mode = clock->archdata.vclock_mode;
95	90	vsyscall_gtod_data.clock.cycle_last = clock->cycle_last;
...	...	@@ -101,7 +96,7 @@
101	96	vsyscall_gtod_data.wall_to_monotonic = *wtm;
102	97	vsyscall_gtod_data.wall_time_coarse = __current_kernel_time();
103	98
104		- write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
	99	+ write_seqcount_end(&vsyscall_gtod_data.seq);
105	100	}
106	101
107	102	static void warn_bad_vsyscall(const char level, struct pt_regs regs,
...	...	@@ -100,12 +100,12 @@
100	100	int mode;
101	101
102	102	do {
103		- seq = read_seqbegin(&gtod->lock);
	103	+ seq = read_seqcount_begin(&gtod->seq);
104	104	mode = gtod->clock.vclock_mode;
105	105	ts->tv_sec = gtod->wall_time_sec;
106	106	ts->tv_nsec = gtod->wall_time_nsec;
107	107	ns = vgetns();
108		- } while (unlikely(read_seqretry(&gtod->lock, seq)));
	108	+ } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
109	109
110	110	timespec_add_ns(ts, ns);
111	111	return mode;
112	112
...	...	@@ -117,13 +117,13 @@
117	117	int mode;
118	118
119	119	do {
120		- seq = read_seqbegin(&gtod->lock);
	120	+ seq = read_seqcount_begin(&gtod->seq);
121	121	mode = gtod->clock.vclock_mode;
122	122	secs = gtod->wall_time_sec;
123	123	ns = gtod->wall_time_nsec + vgetns();
124	124	secs += gtod->wall_to_monotonic.tv_sec;
125	125	ns += gtod->wall_to_monotonic.tv_nsec;
126		- } while (unlikely(read_seqretry(&gtod->lock, seq)));
	126	+ } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
127	127
128	128	/* wall_time_nsec, vgetns(), and wall_to_monotonic.tv_nsec
129	129	* are all guaranteed to be nonnegative.
130	130
...	...	@@ -142,10 +142,10 @@
142	142	{
143	143	unsigned long seq;
144	144	do {
145		- seq = read_seqbegin(&gtod->lock);
	145	+ seq = read_seqcount_begin(&gtod->seq);
146	146	ts->tv_sec = gtod->wall_time_coarse.tv_sec;
147	147	ts->tv_nsec = gtod->wall_time_coarse.tv_nsec;
148		- } while (unlikely(read_seqretry(&gtod->lock, seq)));
	148	+ } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
149	149	return 0;
150	150	}
151	151
152	152
...	...	@@ -153,12 +153,12 @@
153	153	{
154	154	unsigned long seq, ns, secs;
155	155	do {
156		- seq = read_seqbegin(&gtod->lock);
	156	+ seq = read_seqcount_begin(&gtod->seq);
157	157	secs = gtod->wall_time_coarse.tv_sec;
158	158	ns = gtod->wall_time_coarse.tv_nsec;
159	159	secs += gtod->wall_to_monotonic.tv_sec;
160	160	ns += gtod->wall_to_monotonic.tv_nsec;
161		- } while (unlikely(read_seqretry(&gtod->lock, seq)));
	161	+ } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
162	162
163	163	/* wall_time_nsec and wall_to_monotonic.tv_nsec are
164	164	* guaranteed to be between 0 and NSEC_PER_SEC.