Messages in this thread | | | Date | Mon, 13 Dec 2021 21:30:16 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2] perf/core: Fix cgroup event list management |
| |
On Sun, Dec 12, 2021 at 10:59:36PM -0800, Namhyung Kim wrote: > The active cgroup events are managed in the per-cpu cgrp_cpuctx_list. > This list is accessed from current cpu and not protected by any locks. > But from the commit ef54c1a476ae ("perf: Rework > perf_event_exit_event()"), this assumption does not hold true anymore. > > In the perf_remove_from_context(), it can remove an event from the > context without an IPI when the context is not active. I think it
"I tihnk" just doesn't cut it. That means I have to completely reverse engineer your patch and it's assumptions. Which is more work for me :-(
> assumes task event context, but it's possible for cpu event context > only with cgroup events can be inactive at the moment - and it might > become active soon. > > If the event is enabled when it's about to be closed, it might call > perf_cgroup_event_disable() and list_del() with the cgrp_cpuctx_list > on a different cpu. > > This resulted in a crash due to an invalid list pointer access during > the cgroup list traversal on the cpu which the event belongs to. > > The following program can crash my box easily..
Unless that's already public, you've just given the script kiddos ammo, surely we don't need that.
> Let's use IPI to prevent such crashes.
Let's just not do random things and hope stuff 'works'. Either it is correct or it is not.
> Similarly, I think perf_install_in_context() should use IPI for the > cgroup events too.
Let's be sure, ok?
> Reported-by: kernel test robot <lkp@intel.com> # for build error
That's complete garbage, please don't do that.
> Cc: Marco Elver <elver@google.com> > Signed-off-by: Namhyung Kim <namhyung@kernel.org> > --- > v2) simply use IPI for cgroup events > > kernel/events/core.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 30d94f68c5bd..9460c083acd9 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -2388,7 +2388,7 @@ static void perf_remove_from_context(struct perf_event *event, unsigned long fla > * event_function_call() user. > */ > raw_spin_lock_irq(&ctx->lock); > - if (!ctx->is_active) { > + if (!ctx->is_active && !is_cgroup_event(event)) { > __perf_remove_from_context(event, __get_cpu_context(ctx), > ctx, (void *)flags); > raw_spin_unlock_irq(&ctx->lock); > @@ -2857,11 +2857,14 @@ perf_install_in_context(struct perf_event_context *ctx, > * perf_event_attr::disabled events will not run and can be initialized > * without IPI. Except when this is the first event for the context, in > * that case we need the magic of the IPI to set ctx->is_active. > + * Similarly, cgroup events for the context also needs the IPI to > + * manipulate the cgrp_cpuctx_list. > * > * The IOC_ENABLE that is sure to follow the creation of a disabled > * event will issue the IPI and reprogram the hardware. > */ > - if (__perf_effective_state(event) == PERF_EVENT_STATE_OFF && ctx->nr_events) { > + if (__perf_effective_state(event) == PERF_EVENT_STATE_OFF && > + ctx->nr_events && !is_cgroup_event(event)) { > raw_spin_lock_irq(&ctx->lock); > if (ctx->task == TASK_TOMBSTONE) { > raw_spin_unlock_irq(&ctx->lock); > > base-commit: 73743c3b092277febbf69b250ce8ebbca0525aa2
What's junk like that doing ?
| |