From f84a935db47d7f261c025ba9eaa7700261257469 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 29 Nov 2012 22:11:51 +0000 Subject: arm64: vdso: check sequence counter even for coarse realtime operations When returning coarse realtime values from clock_gettime, we must still check the sequence counter to ensure that the kernel does not update the vdso datapage whilst we are loading the coarse timespec as this could potentially result in time appearing to go backwards. This patch delays the coarse realtime check until after we have loaded successfully from the vdso datapage. This does mean that we always load the wtm timespec, but conditionalising the load and adding an extra sequence test is unlikely to buy us anything other than messy code, particularly as the sequence test implies a read barrier. Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S index 05c1229..3a7bdcd 100644 --- a/arch/arm64/kernel/vdso/gettimeofday.S +++ b/arch/arm64/kernel/vdso/gettimeofday.S @@ -124,15 +124,15 @@ ENTRY(__kernel_clock_gettime) 3: seqcnt_acquire ldp x9, x10, [vdso_data, #VDSO_XTIME_CRS_SEC] - cmp w0, #CLOCK_MONOTONIC_COARSE - b.ne 6f - /* Get wtm timespec. */ ldp x14, x15, [vdso_data, #VDSO_WTM_CLK_SEC] /* Check the sequence counter. */ seqcnt_read w13 seqcnt_check w13, 3b + + cmp w0, #CLOCK_MONOTONIC_COARSE + b.ne 6f 4: /* Add on wtm timespec. */ add x9, x9, x14 -- cgit v0.10.2