On Wed, 15 Mar 2023 17:43:13 +0800 Yicong Yang <yangyicong@xxxxxxxxxx> wrote: > From: Yicong Yang <yangyicong@xxxxxxxxxxxxx> > > perf will try to start PTT trace on every CPU presented in cpumask sysfs > attribute and it will fail to start on offline CPUs(see the comments in > perf_event_open()). But the driver is using cpumask_of_node() to export > the available cpumask which may include offline CPUs and may fail the > perf unintendedly. Fix this by only export the online CPUs of the node. There isn't clear documentation that I can find for cpumask_of_node() and chasing through on arm64 (which is what we care about for this driver) it's maintained via numa_add_cpu() numa_remove_cpu() Those are called in arch/arm64/kernel/smp.c in locations that are closely coupled with set_cpu_online(cpu, XXX); https://elixir.bootlin.com/linux/v6.3-rc4/source/arch/arm64/kernel/smp.c#L246 https://elixir.bootlin.com/linux/v6.3-rc4/source/arch/arm64/kernel/smp.c#L303 Now there are races when the two might not be in sync but in this case we are just exposing the result to userspace, so chances of a race after this sysfs attribute has been read seems much higher to me and I don't think we can do anything about that. Is there another path that I'm missing where online and node masks are out of sync? Jonathan > > Fixes: ff0de066b463 ("hwtracing: hisi_ptt: Add trace function support for HiSilicon PCIe Tune and Trace device") > Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx> > --- > drivers/hwtracing/ptt/hisi_ptt.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/drivers/hwtracing/ptt/hisi_ptt.c b/drivers/hwtracing/ptt/hisi_ptt.c > index 30f1525639b5..0a10c7ec46ad 100644 > --- a/drivers/hwtracing/ptt/hisi_ptt.c > +++ b/drivers/hwtracing/ptt/hisi_ptt.c > @@ -487,9 +487,18 @@ static ssize_t cpumask_show(struct device *dev, struct device_attribute *attr, > char *buf) > { > struct hisi_ptt *hisi_ptt = to_hisi_ptt(dev_get_drvdata(dev)); > - const cpumask_t *cpumask = cpumask_of_node(dev_to_node(&hisi_ptt->pdev->dev)); > + cpumask_var_t mask; > + ssize_t n; > > - return cpumap_print_to_pagebuf(true, buf, cpumask); > + if (!alloc_cpumask_var(&mask, GFP_KERNEL)) > + return 0; > + > + cpumask_and(mask, cpumask_of_node(dev_to_node(&hisi_ptt->pdev->dev)), > + cpu_online_mask); > + n = cpumap_print_to_pagebuf(true, buf, mask); > + free_cpumask_var(mask); > + > + return n; > } > static DEVICE_ATTR_RO(cpumask); >
