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| author | Chris Wilson <chris@chris-wilson.co.uk> | 2020-01-23 21:08:49 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2020-03-06 14:57:16 +0300 |
| commit | f1dfdab694eb3838ac26f4b73695929c07d92a33 (patch) | |
| tree | 37791cfddf0e1e76792321e96271bf86cbe9c5bf /kernel/sched | |
| parent | 1b10d388d094bb32129060236add6f50b204a69d (diff) | |
| download | linux-f1dfdab694eb3838ac26f4b73695929c07d92a33.tar.xz | |
sched/vtime: Prevent unstable evaluation of WARN(vtime->state)
As the vtime is sampled under loose seqcount protection by kcpustat, the
vtime fields may change as the code flows. Where logic dictates a field
has a static value, use a READ_ONCE.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Fixes: 74722bb223d0 ("sched/vtime: Bring up complete kcpustat accessor")
Link: https://lkml.kernel.org/r/20200123180849.28486-1-frederic@kernel.org
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/cputime.c | 41 |
1 files changed, 22 insertions, 19 deletions
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index cff3e656566d..dac9104d126f 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -909,8 +909,10 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 *stime) } while (read_seqcount_retry(&vtime->seqcount, seq)); } -static int vtime_state_check(struct vtime *vtime, int cpu) +static int vtime_state_fetch(struct vtime *vtime, int cpu) { + int state = READ_ONCE(vtime->state); + /* * We raced against a context switch, fetch the * kcpustat task again. @@ -927,10 +929,10 @@ static int vtime_state_check(struct vtime *vtime, int cpu) * * Case 1) is ok but 2) is not. So wait for a safe VTIME state. */ - if (vtime->state == VTIME_INACTIVE) + if (state == VTIME_INACTIVE) return -EAGAIN; - return 0; + return state; } static u64 kcpustat_user_vtime(struct vtime *vtime) @@ -949,14 +951,15 @@ static int kcpustat_field_vtime(u64 *cpustat, { struct vtime *vtime = &tsk->vtime; unsigned int seq; - int err; do { + int state; + seq = read_seqcount_begin(&vtime->seqcount); - err = vtime_state_check(vtime, cpu); - if (err < 0) - return err; + state = vtime_state_fetch(vtime, cpu); + if (state < 0) + return state; *val = cpustat[usage]; @@ -969,7 +972,7 @@ static int kcpustat_field_vtime(u64 *cpustat, */ switch (usage) { case CPUTIME_SYSTEM: - if (vtime->state == VTIME_SYS) + if (state == VTIME_SYS) *val += vtime->stime + vtime_delta(vtime); break; case CPUTIME_USER: @@ -981,11 +984,11 @@ static int kcpustat_field_vtime(u64 *cpustat, *val += kcpustat_user_vtime(vtime); break; case CPUTIME_GUEST: - if (vtime->state == VTIME_GUEST && task_nice(tsk) <= 0) + if (state == VTIME_GUEST && task_nice(tsk) <= 0) *val += vtime->gtime + vtime_delta(vtime); break; case CPUTIME_GUEST_NICE: - if (vtime->state == VTIME_GUEST && task_nice(tsk) > 0) + if (state == VTIME_GUEST && task_nice(tsk) > 0) *val += vtime->gtime + vtime_delta(vtime); break; default: @@ -1036,23 +1039,23 @@ static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst, { struct vtime *vtime = &tsk->vtime; unsigned int seq; - int err; do { u64 *cpustat; u64 delta; + int state; seq = read_seqcount_begin(&vtime->seqcount); - err = vtime_state_check(vtime, cpu); - if (err < 0) - return err; + state = vtime_state_fetch(vtime, cpu); + if (state < 0) + return state; *dst = *src; cpustat = dst->cpustat; /* Task is sleeping, dead or idle, nothing to add */ - if (vtime->state < VTIME_SYS) + if (state < VTIME_SYS) continue; delta = vtime_delta(vtime); @@ -1061,15 +1064,15 @@ static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst, * Task runs either in user (including guest) or kernel space, * add pending nohz time to the right place. */ - if (vtime->state == VTIME_SYS) { + if (state == VTIME_SYS) { cpustat[CPUTIME_SYSTEM] += vtime->stime + delta; - } else if (vtime->state == VTIME_USER) { + } else if (state == VTIME_USER) { if (task_nice(tsk) > 0) cpustat[CPUTIME_NICE] += vtime->utime + delta; else cpustat[CPUTIME_USER] += vtime->utime + delta; } else { - WARN_ON_ONCE(vtime->state != VTIME_GUEST); + WARN_ON_ONCE(state != VTIME_GUEST); if (task_nice(tsk) > 0) { cpustat[CPUTIME_GUEST_NICE] += vtime->gtime + delta; cpustat[CPUTIME_NICE] += vtime->gtime + delta; @@ -1080,7 +1083,7 @@ static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst, } } while (read_seqcount_retry(&vtime->seqcount, seq)); - return err; + return 0; } void kcpustat_cpu_fetch(struct kernel_cpustat *dst, int cpu) |