linux-kernel - [PATCH] timekeeping/vsyscall: Update vdso data unconditionally

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Date:   Thu, 24 Oct 2019 11:28:29 +0800
From:   Huacai Chen <chenhc@...ote.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        chenhuacai@...il.com, linux-kernel@...r.kernel.org,
        Huacai Chen <chenhc@...ote.com>, stable@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Paul Burton <paul.burton@...s.com>, linux-mips@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH] timekeeping/vsyscall: Update vdso data unconditionally

In do_hres(), we currently use whether the return value of __arch_get_
hw_counter() is negative to indicate fallback, but MIPS returns 0 when
clock_mode is invalid.

It is sure that MIPS has a bug when clock_mode is invalid and should
return ULL_MAX as ARM64 does (Vincenzo has already submitted a patch).
But at the time we found another bug: currently update_vsyscall() and
update_vsyscall_tz() rely on __arch_use_vsyscall() to update the vdso
data, which causes __cvdso_clock_getres() and some other functions get
wrong results when clock_mode is invalid. So, in this patch we update
vdso data unconditionally.

Fixes: 44f57d788e7deecb50 ("timekeeping: Provide a generic update_vsyscall() implementation")
Cc: stable@...r.kernel.org
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Paul Burton <paul.burton@...s.com>
Cc: linux-mips@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org
Signed-off-by: Huacai Chen <chenhc@...ote.com>
---
 kernel/time/vsyscall.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
index 4bc37ac..5ee0f77 100644
--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -110,8 +110,7 @@ void update_vsyscall(struct timekeeper *tk)
 	nsec		= nsec + tk->wall_to_monotonic.tv_nsec;
 	vdso_ts->sec	+= __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec);
 
-	if (__arch_use_vsyscall(vdata))
-		update_vdso_data(vdata, tk);
+	update_vdso_data(vdata, tk);
 
 	__arch_update_vsyscall(vdata, tk);
 
@@ -124,10 +123,8 @@ void update_vsyscall_tz(void)
 {
 	struct vdso_data *vdata = __arch_get_k_vdso_data();
 
-	if (__arch_use_vsyscall(vdata)) {
-		vdata[CS_HRES_COARSE].tz_minuteswest = sys_tz.tz_minuteswest;
-		vdata[CS_HRES_COARSE].tz_dsttime = sys_tz.tz_dsttime;
-	}
+	vdata[CS_HRES_COARSE].tz_minuteswest = sys_tz.tz_minuteswest;
+	vdata[CS_HRES_COARSE].tz_dsttime = sys_tz.tz_dsttime;
 
 	__arch_sync_vdso_data(vdata);
 }
-- 
2.7.0