From 3da4390bcdf4dcea5eb7961f1ba05f75c642a39d Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 4 Jan 2022 14:57:14 +0000 Subject: [PATCH] arm64: perf: Don't register user access sysctl handler multiple times Commit e2012600810c ("arm64: perf: Add userspace counter access disable switch") introduced a new 'perf_user_access' sysctl file to enable and disable direct userspace access to the PMU counters. Sadly, Geert reports that on his big.LITTLE SoC ('Renesas Salvator-XS w/ R-Car H3'), the file is created for each PMU type probed, resulting in a splat during boot: | hw perfevents: enabled with armv8_cortex_a53 PMU driver, 7 counters available | sysctl duplicate entry: /kernel//perf_user_access | CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.16.0-rc3-arm64-renesas-00003-ge2012600810c #1420 | Hardware name: Renesas Salvator-X 2nd version board based on r8a77951 (DT) | Call trace: | dump_backtrace+0x0/0x190 | show_stack+0x14/0x20 | dump_stack_lvl+0x88/0xb0 | dump_stack+0x14/0x2c | __register_sysctl_table+0x384/0x818 | register_sysctl+0x20/0x28 | armv8_pmu_init.constprop.0+0x118/0x150 | armv8_a57_pmu_init+0x1c/0x28 | arm_pmu_device_probe+0x1b4/0x558 | armv8_pmu_device_probe+0x18/0x20 | platform_probe+0x64/0xd0 | hw perfevents: enabled with armv8_cortex_a57 PMU driver, 7 counters available Introduce a state variable to track creation of the sysctl file and ensure that it is only created once. Reported-by: Geert Uytterhoeven Fixes: e2012600810c ("arm64: perf: Add userspace counter access disable switch") Link: https://lore.kernel.org/r/CAMuHMdVcDxR9sGzc5pcnORiotonERBgc6dsXZXMd6wTvLGA9iw@mail.gmail.com Signed-off-by: Will Deacon --- arch/arm64/kernel/perf_event.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c index 4c5c8d7..cab678e 100644 --- a/arch/arm64/kernel/perf_event.c +++ b/arch/arm64/kernel/perf_event.c @@ -1214,6 +1214,14 @@ static struct ctl_table armv8_pmu_sysctl_table[] = { { } }; +static void armv8_pmu_register_sysctl_table(void) +{ + static u32 tbl_registered = 0; + + if (!cmpxchg_relaxed(&tbl_registered, 0, 1)) + register_sysctl("kernel", armv8_pmu_sysctl_table); +} + static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name, int (*map_event)(struct perf_event *event), const struct attribute_group *events, @@ -1248,8 +1256,7 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name, cpu_pmu->attr_groups[ARMPMU_ATTR_GROUP_CAPS] = caps ? caps : &armv8_pmuv3_caps_attr_group; - register_sysctl("kernel", armv8_pmu_sysctl_table); - + armv8_pmu_register_sysctl_table(); return 0; } -- 2.7.4