Messages in this thread | | | Date | Wed, 23 Nov 2022 23:26:43 +0800 | From | Pengfei Xu <> | Subject | Re: [Syzkaller & bisect] There is "__perf_event_overflow" WARNING in v6.1-rc5 kernel in guest |
| |
Hi Peter,
On 2022-11-23 at 16:05:14 +0100, Peter Zijlstra wrote: > On Sat, Nov 19, 2022 at 10:45:54AM +0800, Pengfei Xu wrote: > > > The result shows that your additional patch fixed this issue! > > If possible, could you add Reported-and-tested-by tag from me. > > After talking with Marco for a bit the patch now looks like the below. > I've tentatively retained your tested-by, except of course, you haven't. > > If I could bother you once more to test the branch: > > git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git perf/urgent > Yes, sure, it's my pleasure! I will clone and test the origin/perf/urgent branch in this repo and update the email soon. git clone git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git time out in my side, and I git cloned https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git, it should be the same repo.
Thanks! BR.
> --- > Subject: perf: Consider OS filter fail > From: Peter Zijlstra <peterz@infradead.org> > Date: Sat, 19 Nov 2022 10:45:54 +0800 > > Some PMUs (notably the traditional hardware kind) have boundary issues > with the OS filter. Specifically, it is possible for > perf_event_attr::exclude_kernel=1 events to trigger in-kernel due to > SKID or errata. > > This can upset the sigtrap logic some and trigger the WARN. > > However, if this invalid sample is the first we must not loose the > SIGTRAP, OTOH if it is the second, it must not override the > pending_addr with an invalid one. > > Fixes: ca6c21327c6a ("perf: Fix missing SIGTRAPs") > Reported-by: Pengfei Xu <pengfei.xu@intel.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Tested-by: Pengfei Xu <pengfei.xu@intel.com> > Link: https://lkml.kernel.org/r/Y3hDYiXwRnJr8RYG@xpf.sh.intel.com > --- > kernel/events/core.c | 24 ++++++++++++++++++++++-- > 1 file changed, 22 insertions(+), 2 deletions(-) > > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -9273,6 +9273,19 @@ int perf_event_account_interrupt(struct > return __perf_event_account_interrupt(event, 1); > } > > +static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *regs) > +{ > + /* > + * Due to interrupt latency (AKA "skid"), we may enter the > + * kernel before taking an overflow, even if the PMU is only > + * counting user events. > + */ > + if (event->attr.exclude_kernel && !user_mode(regs)) > + return false; > + > + return true; > +} > + > /* > * Generic event overflow handling, sampling. > */ > @@ -9306,6 +9319,13 @@ static int __perf_event_overflow(struct > } > > if (event->attr.sigtrap) { > + /* > + * The desired behaviour of sigtrap vs invalid samples is a bit > + * tricky; on the one hand, one should not loose the SIGTRAP if > + * it is the first event, on the other hand, we should also not > + * trigger the WARN or override the data address. > + */ > + bool valid_sample = sample_is_allowed(event, regs); > unsigned int pending_id = 1; > > if (regs) > @@ -9313,7 +9333,7 @@ static int __perf_event_overflow(struct > if (!event->pending_sigtrap) { > event->pending_sigtrap = pending_id; > local_inc(&event->ctx->nr_pending); > - } else if (event->attr.exclude_kernel) { > + } else if (event->attr.exclude_kernel && valid_sample) { > /* > * Should not be able to return to user space without > * consuming pending_sigtrap; with exceptions: > @@ -9330,7 +9350,7 @@ static int __perf_event_overflow(struct > } > > event->pending_addr = 0; > - if (data->sample_flags & PERF_SAMPLE_ADDR) > + if (valid_sample && (data->sample_flags & PERF_SAMPLE_ADDR)) > event->pending_addr = data->addr; > irq_work_queue(&event->pending_irq); > }
| |