Messages in this thread | | | Date | Wed, 18 Mar 2020 19:05:35 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2] perf/core: install cgroup events to correct cpuctx |
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On Wed, Mar 18, 2020 at 07:07:29AM +0000, Song Liu wrote: > Hi Peter, > > > On Mar 5, 2020, at 11:48 PM, Song Liu <songliubraving@fb.com> wrote: > > > > > > > >> On Jan 24, 2020, at 1:15 AM, Peter Zijlstra <peterz@infradead.org> wrote: > >> > >> On Wed, Jan 22, 2020 at 11:50:27AM -0800, Song Liu wrote: > >>> cgroup events are always installed in the cpuctx. However, when it is not > >>> installed via IPI, list_update_cgroup_event() adds it to cpuctx of current > >>> CPU, which triggers the following with CONFIG_DEBUG_LIST: > >>> > >> > >>> [ 31.777570] list_add double add: new=ffff888ff7cf0db0, prev=ffff888ff7ce82f0, next=ffff888ff7cf0db0. > >> > >>> To reproduce this, we can simply run: > >>> perf stat -e cs -a & > >>> perf stat -e cs -G anycgroup > >>> > >>> Fix this by installing it to cpuctx that contains event->ctx, and the > >>> proper cgrp_cpuctx_list. > >>> > >>> Fixes: db0503e4f675 ("perf/core: Optimize perf_install_in_event()") > >>> Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> > >>> Cc: Andi Kleen <andi@firstfloor.org> > >>> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> > >>> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> > >>> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> > >>> Cc: Jiri Olsa <jolsa@redhat.com> > >>> Cc: Namhyung Kim <namhyung@kernel.org> > >>> Cc: Thomas Gleixner <tglx@linutronix.de> > >>> Signed-off-by: Song Liu <songliubraving@fb.com> > >> > >> Thanks! > > > > I just realized this won't fully fix the problem, because later in > > list_update_cgroup_event() we use "current": > > > > struct perf_cgroup *cgrp = perf_cgroup_from_task(current, ctx); > > Could you please share your thoughts on this? I think we cannot use current > in list_update_cgroup_event(), unless we call it on the target CPU.
Bah, that cgroup crap is 'wrong'. It's pointless to track the cpuctx->cgrp state for disabled events.
Let me see if I can unravel that crud.
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