Messages in this thread | | | Date | Thu, 27 Feb 2020 14:34:08 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH] sched/vtime: Prevent unstable evaluation of WARN(vtime->state) |
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Ping (again)?
On Thu, Jan 23, 2020 at 07:08:49PM +0100, Frederic Weisbecker wrote: > From: Chris Wilson <chris@chris-wilson.co.uk> > > 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. > > Fixes: 74722bb223d0 ("sched/vtime: Bring up complete kcpustat accessor") > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Ingo Molnar <mingo@kernel.org> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org> > --- > kernel/sched/cputime.c | 41 ++++++++++++++++++++++------------------- > 1 file changed, 22 insertions(+), 19 deletions(-) > > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c > index d43318a489f2..df3577149d2e 100644 > --- a/kernel/sched/cputime.c > +++ b/kernel/sched/cputime.c > @@ -912,8 +912,10 @@ 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. > @@ -930,10 +932,10 @@ 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) > @@ -952,14 +954,15 @@ 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]; > > @@ -972,7 +975,7 @@ 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: > @@ -984,11 +987,11 @@ 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: > @@ -1039,23 +1042,23 @@ 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); > @@ -1064,15 +1067,15 @@ 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; > @@ -1083,7 +1086,7 @@ 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) > -- > 2.25.0 >
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