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arm64: perf: Don't register user access sysctl handler multiple times

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Commit e201260081 ("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 <geert@linux-m68k.org>
Fixes: e201260081 ("arm64: perf: Add userspace counter access disable switch")
Link: https://lore.kernel.org/r/CAMuHMdVcDxR9sGzc5pcnORiotonERBgc6dsXZXMd6wTvLGA9iw@mail.gmail.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Will Deacon 2022-01-04 14:57:14 +00:00
parent 2da56881a7
commit 3da4390bcd
1 changed files with 9 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
arch/arm64/kernel/perf_event.c
View File

@ -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;
}