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| author | Will Deacon <will.deacon@arm.com> | 2012-11-29 22:11:51 +0000 |
|---|---|---|
| committer | Catalin Marinas <catalin.marinas@arm.com> | 2012-12-05 11:20:03 +0000 |
| commit | f84a935db47d7f261c025ba9eaa7700261257469 (patch) | |
| tree | 0df122141ab5862220184f5f6746038daf925cf3 | |
| parent | 251db45336c8fb5fd0c36f71aabc6950e427110f (diff) | |
| download | linux-stable-f84a935db47d7f261c025ba9eaa7700261257469.tar.gz linux-stable-f84a935db47d7f261c025ba9eaa7700261257469.tar.bz2 linux-stable-f84a935db47d7f261c025ba9eaa7700261257469.zip | |
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 <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
| -rw-r--r-- | arch/arm64/kernel/vdso/gettimeofday.S | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S index 05c1229a2874..3a7bdcd55ab6 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 |