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Commite201260081("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.