On 2023/3/29 0:24, Jonathan Cameron wrote: > 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? > maybe no. This patch maybe incorrect and I need more investigation, so let's me drop it from the series. Tested and everything seems fine now. I found this problem and referred to commit 064f0e9302af ("mm: only display online cpus of the numa node") which might be the same problem. But seems unnecessary that cpumask_of_node() already include online CPUs only. Thanks. > 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); >> > > . >
