arm64: vdso: remove broken, redundant sequence counting for timezones

This patch is an arm64 version of ce73ec6db47a ("powerpc/vdso: Remove
redundant locking in update_vsyscall_tz()").

Timezone data is not protected, so the sequence counter is not required
to ensure consistency. Furthermore, having multiple paths updating the
counter leads to a race between update_vsyscall and update_vsyscall_tz,
so remove the timezone sequence counting from both the kernel and the
vdso.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index c958cb8..6a389dc 100644 (file)
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -252,10 +252,6 @@ void update_vsyscall(struct timekeeper *tk)
 
 void update_vsyscall_tz(void)
 {
-       ++vdso_data->tb_seq_count;
-       smp_wmb();
        vdso_data->tz_minuteswest       = sys_tz.tz_minuteswest;
        vdso_data->tz_dsttime           = sys_tz.tz_dsttime;
-       smp_wmb();
-       ++vdso_data->tb_seq_count;
 }

diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
index 8bf658d..f0a6d10 100644 (file)
--- a/arch/arm64/kernel/vdso/gettimeofday.S
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -73,8 +73,6 @@ ENTRY(__kernel_gettimeofday)
        /* If tz is NULL, return 0. */
        cbz     x1, 3f
        ldp     w4, w5, [vdso_data, #VDSO_TZ_MINWEST]
-       seqcnt_read w9
-       seqcnt_check w9, 1b
        stp     w4, w5, [x1, #TZ_MINWEST]
 3:
        mov     x0, xzr